< draft-leiba-imap-implement-guide-07.txt   draft-leiba-imap-implement-guide-08.txt >
Network Working Group B. Leiba Network Working Group B. Leiba
Internet Draft IBM T.J. Watson Research Center Internet Draft IBM T.J. Watson Research Center
Document: draft-leiba-imap-implement-guide-07.txt May 1998 Document: draft-leiba-imap-implement-guide-08.txt December 1998
Expires October 1998 Expires June 1999
IMAP4 Implementation Recommendations IMAP4 Implementation Recommendations
Status of this Document Status of this Document
This document provides information for the Internet community. This This document provides information for the Internet community. This
document does not specify an Internet standard of any kind. document does not specify an Internet standard of any kind.
Distribution of this document is unlimited. Distribution of this document is unlimited.
This document is an Internet Draft. Internet Drafts are working This document is an Internet Draft. Internet Drafts are working
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draft" or "work in progress". draft" or "work in progress".
To view the entire list of current Internet-Drafts, please check the To view the entire list of current Internet-Drafts, please check the
"1id-abstracts.txt" listing contained in the Internet-Drafts Shadow "1id-abstracts.txt" listing contained in the Internet-Drafts Shadow
Directories on ftp.is.co.za (Africa), ftp.nordu.net (Northern Directories on ftp.is.co.za (Africa), ftp.nordu.net (Northern
Europe), ftp.nis.garr.it (Southern Europe), munnari.oz.au (Pacific Europe), ftp.nis.garr.it (Southern Europe), munnari.oz.au (Pacific
Rim), ftp.ietf.org (US East Coast), or ftp.isi.edu (US West Coast). Rim), ftp.ietf.org (US East Coast), or ftp.isi.edu (US West Coast).
A revised version of this draft document will be submitted to the RFC A revised version of this draft document will be submitted to the RFC
editor. Discussion and suggestions for improvement are requested. editor. Discussion and suggestions for improvement are requested.
This document will expire by the end of October 1998. This document will expire by the end of June 1999.
1. Abstract 1. Abstract
The IMAP4 specification [RFC-2060] describes a rich protocol for use The IMAP4 specification [RFC-2060] describes a rich protocol for use
in building clients and servers for storage, retrieval, and in building clients and servers for storage, retrieval, and
manipulation of electronic mail. Because the protocol is so rich and manipulation of electronic mail. Because the protocol is so rich and
has so many implementation choices, there are often trade-offs that has so many implementation choices, there are often trade-offs that
must be made and issues that must be considered when designing such must be made and issues that must be considered when designing such
clients and servers. This document attempts to outline these issues clients and servers. This document attempts to outline these issues
and to make recommendations in order to make the end products as and to make recommendations in order to make the end products as
interoperable as possible. interoperable as possible.
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2. Conventions used in this document 2. Conventions used in this document
In examples, "C:" indicates lines sent by a client that is connected In examples, "C:" indicates lines sent by a client that is connected
to a server. "S:" indicates lines sent by the server to the client. to a server. "S:" indicates lines sent by the server to the client.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC-2119]. document are to be interpreted as described in [RFC-2119].
3. Interoperability Issues and Recommendations 3. Interoperability Issues and Recommendations
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read mail from a client at home while the client in the office is read mail from a client at home while the client in the office is
still connected; or the help desk staff can all work out of the same still connected; or the help desk staff can all work out of the same
inbox, all seeing the same pool of questions. An important point inbox, all seeing the same pool of questions. An important point
about this capability, though is that NO SERVER IS GUARANTEED TO about this capability, though is that NO SERVER IS GUARANTEED TO
SUPPORT THIS. If you are selecting an IMAP server and this facility SUPPORT THIS. If you are selecting an IMAP server and this facility
is important to you, be sure that the server you choose to install, is important to you, be sure that the server you choose to install,
in the configuration you choose to use, supports it. in the configuration you choose to use, supports it.
If you are designing a client, you MUST NOT assume that you can If you are designing a client, you MUST NOT assume that you can
access the same mailbox more than once at a time. That means access the same mailbox more than once at a time. That means
1. you must handle gracefully the failure of a SELECT command if 1. you MUST handle gracefully the failure of a SELECT command if
the server refuses the second SELECT, the server refuses the second SELECT,
2. you must handle reasonably the severing of your connection (see 2. you MUST handle reasonably the severing of your connection (see
"Severed Connections", below) if the server chooses to allow the "Severed Connections", below) if the server chooses to allow the
second SELECT by forcing the first off, second SELECT by forcing the first off,
3. you must avoid making multiple connections to the same mailbox 3. you MUST avoid making multiple connections to the same mailbox
in your own client (for load balancing or other such reasons), in your own client (for load balancing or other such reasons),
and and
4. you must avoid using the STATUS command on a mailbox that you 4. you MUST avoid using the STATUS command on a mailbox that you
have selected (with some server implementations the STATUS have selected (with some server implementations the STATUS
command has the same problems with multiple access as do the command has the same problems with multiple access as do the
SELECT and EXAMINE commands). SELECT and EXAMINE commands).
A further note about STATUS: The STATUS command is sometimes used to A further note about STATUS: The STATUS command is sometimes used to
check a non-selected mailbox for new mail. This mechanism MUST NOT check a non-selected mailbox for new mail. This mechanism MUST NOT
be used to check for new mail in the selected mailbox; section 5.2 of be used to check for new mail in the selected mailbox; section 5.2 of
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[RFC-2060] specifically forbids this in its last paragraph. Further, [RFC-2060] specifically forbids this in its last paragraph. Further,
since STATUS takes a mailbox name it is an independent operation, not since STATUS takes a mailbox name it is an independent operation, not
operating on the selected mailbox. Because of this, the information operating on the selected mailbox. Because of this, the information
it returns is not necessarily in synchronization with the selected it returns is not necessarily in synchronization with the selected
mailbox state. mailbox state.
3.1.2. Severed Connections 3.1.2. Severed Connections
The client/server connection may be severed for one of three reasons: The client/server connection may be severed for one of three reasons:
the client severs the connection, the server severs the connection, the client severs the connection, the server severs the connection,
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When the server wants to sever a connection it's usually due to an When the server wants to sever a connection it's usually due to an
inactivity timeout or is because a situation has arisen that has inactivity timeout or is because a situation has arisen that has
changed the state of the mail store in a way that the server can not changed the state of the mail store in a way that the server can not
communicate to the client. The server SHOULD send an untagged BYE communicate to the client. The server SHOULD send an untagged BYE
response to the client and then close the socket. Sending an response to the client and then close the socket. Sending an
untagged BYE response before severing allows the server to send a untagged BYE response before severing allows the server to send a
human-readable explanation of the problem to the client, which the human-readable explanation of the problem to the client, which the
client may then log, display to the user, or both (see section 7.1.5 client may then log, display to the user, or both (see section 7.1.5
of [RFC-2060]). of [RFC-2060]).
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Regarding inactivity timeouts, there is some controversy. Unlike
POP, for which the design is for a client to connect, retrieve mail,
and log out, IMAP<RIGHT SINGLE QUOTATION MARK>s design encourages long-lived (and mostly
inactive) client/server sessions. As the number of users grows, this
can use up a lot of server resources, especially with clients that
are designed to maintain sessions for mailboxes that the user has
finished accessing. To alleviate this, a server MAY implement an
inactivity timeout, unilaterally closing a session (after first
sending an untagged BYE, as noted above). Some server operators have
reported dramatic improvements in server performance after doing
this. As specified in [RFC-2060], if such a timeout is done it MUST
NOT be until at least 30 minutes of inactivity. The reason for this
specification is to prevent clients from sending commands (such as
NOOP) to the server at frequent intervals simply to avert a too-early
timeout. If the client knows that the server may not time out the
session for at least 30 minutes, then the client need not poll at
intervals more frequent than, say, 25 minutes.
3.2. Scaling 3.2. Scaling
IMAP4 has many features that allow for scalability, as mail stores IMAP4 has many features that allow for scalability, as mail stores
become larger and more numerous. Large numbers of users, mailboxes, become larger and more numerous. Large numbers of users, mailboxes,
and messages, and very large messages require thought to handle and messages, and very large messages require thought to handle
efficiently. This document will not address the administrative efficiently. This document will not address the administrative
issues involved in large numbers of users, but we will look at the issues involved in large numbers of users, but we will look at the
other items. other items.
3.2.1. Flood Control 3.2.1. Flood Control
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reduce that danger. reduce that danger.
There is also the case where a client can flood a server, by sending There is also the case where a client can flood a server, by sending
an arbitratily long command. We'll discuss that issue, too, in this an arbitratily long command. We'll discuss that issue, too, in this
section. section.
3.2.1.1. Listing Mailboxes 3.2.1.1. Listing Mailboxes
Some servers present Usenet newsgroups to IMAP users. Newsgroups, Some servers present Usenet newsgroups to IMAP users. Newsgroups,
and other such hierarchical mailbox structures, can be very numerous and other such hierarchical mailbox structures, can be very numerous
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but may have only a few entries at the top level of hierarchy. Also, but may have only a few entries at the top level of hierarchy. Also,
some servers are built against mail stores that can, unbeknownst to some servers are built against mail stores that can, unbeknownst to
the server, have circular hierarchies - that is, it's possible for the server, have circular hierarchies - that is, it's possible for
"a/b/c/d" to resolve to the same file structure as "a", which would "a/b/c/d" to resolve to the same file structure as "a", which would
then mean that "a/b/c/d/b" is the same as "a/b", and the hierarchy then mean that "a/b/c/d/b" is the same as "a/b", and the hierarchy
will never end. The LIST response in this case will be unlimited. will never end. The LIST response in this case will be unlimited.
Clients that will have trouble with this are those that use Clients that will have trouble with this are those that use
C: 001 LIST "" * C: 001 LIST "" *
to determine the mailbox list. Because of this, clients SHOULD NOT to determine the mailbox list. Because of this, clients SHOULD NOT
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3.2.1.2. Fetching the List of Messages 3.2.1.2. Fetching the List of Messages
When a client selects a mailbox, it is given a count, in the untagged When a client selects a mailbox, it is given a count, in the untagged
EXISTS response, of the messages in the mailbox. This number can be EXISTS response, of the messages in the mailbox. This number can be
very large. In such a case it might be unwise to use very large. In such a case it might be unwise to use
C: 004 FETCH 1:* ALL C: 004 FETCH 1:* ALL
to populate the user's view of the mailbox. One good method to avoid to populate the user's view of the mailbox. One good method to avoid
problems with this is to batch the requests, thus: problems with this is to batch the requests, thus:
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C: 004 FETCH 1:50 ALL C: 004 FETCH 1:50 ALL
S: * 1 FETCH ...etc... S: * 1 FETCH ...etc...
S: 004 OK done S: 004 OK done
C: 005 FETCH 51:100 ALL C: 005 FETCH 51:100 ALL
S: * 51 FETCH ...etc... S: * 51 FETCH ...etc...
S: 005 OK done S: 005 OK done
C: 006 FETCH 101:150 ALL C: 006 FETCH 101:150 ALL
...etc... ...etc...
Using this method, another command, such as "FETCH 6 BODY[1]" can be Using this method, another command, such as "FETCH 6 BODY[1]" can be
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want to present various sort orders to the user (by subject, by date want to present various sort orders to the user (by subject, by date
sent, by sender, and so on) and in that case (lacking a SORT sent, by sender, and so on) and in that case (lacking a SORT
extension on the server side) the client WILL have to retrieve all extension on the server side) the client WILL have to retrieve all
message descriptors. A client that provides this service SHOULD NOT message descriptors. A client that provides this service SHOULD NOT
do it by default and SHOULD inform the user of the costs of choosing do it by default and SHOULD inform the user of the costs of choosing
this option for large mailboxes. this option for large mailboxes.
3.2.1.3. Fetching a Large Body Part 3.2.1.3. Fetching a Large Body Part
The issue here is similar to the one for a list of messages. In the The issue here is similar to the one for a list of messages. In the
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BODYSTRUCTURE response the client knows the size, in bytes, of the BODYSTRUCTURE response the client knows the size, in bytes, of the
body part it plans to fetch. Suppose this is a 70 MB video clip. body part it plans to fetch. Suppose this is a 70 MB video clip.
The client can use partial fetches to retrieve the body part in The client can use partial fetches to retrieve the body part in
pieces, avoiding the problem of an uninterruptible 70 MB literal pieces, avoiding the problem of an uninterruptible 70 MB literal
coming back from the server: coming back from the server:
C: 022 FETCH 3 BODY[1]<0.20000> C: 022 FETCH 3 BODY[1]<0.20000>
S: * 3 FETCH (FLAGS(\Seen) BODY[1]<0> {20000} S: * 3 FETCH (FLAGS(\Seen) BODY[1]<0> {20000}
S: ...data...) S: ...data...)
S: 022 OK done S: 022 OK done
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forcing the transfer of all body parts when the user might only want forcing the transfer of all body parts when the user might only want
to see some of them - a user logged on by modem and reading a small to see some of them - a user logged on by modem and reading a small
text message with a large ZIP file attached may prefer to read the text message with a large ZIP file attached may prefer to read the
text only and save the ZIP file for later. Therefore, a client text only and save the ZIP file for later. Therefore, a client
SHOULD NOT normally retrieve entire messages and SHOULD retrieve SHOULD NOT normally retrieve entire messages and SHOULD retrieve
message body parts selectively. message body parts selectively.
3.2.1.5. Long Command Lines 3.2.1.5. Long Command Lines
A client can wind up building a very long command line in an effort A client can wind up building a very long command line in an effort
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to try to be efficient about requesting information from a server. to try to be efficient about requesting information from a server.
This can typically happen when a client builds a message set from This can typically happen when a client builds a message set from
selected messages and doesn't recognise that contiguous blocks of selected messages and doesn't recognise that contiguous blocks of
messages may be group in a range. Suppose a user selects all 10,000 messages may be group in a range. Suppose a user selects all 10,000
messages in a large mailbox and then unselects message 287. The messages in a large mailbox and then unselects message 287. The
client could build that message set as "1:286,288:10000", but a client could build that message set as "1:286,288:10000", but a
client that doesn't handle that might try to enumerate each message client that doesn't handle that might try to enumerate each message
individually and build "1,2,3,4, [and so on] ,9999,10000". Adding individually and build "1,2,3,4, [and so on] ,9999,10000". Adding
that to the fetch command results in a command line that's almost that to the fetch command results in a command line that's almost
49,000 octets long, and, clearly, one can construct a command line 49,000 octets long, and, clearly, one can construct a command line
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The client isn't the only entity that can get flooded: the end user, The client isn't the only entity that can get flooded: the end user,
too, may need some flood control. The IMAP4 protocol provides such too, may need some flood control. The IMAP4 protocol provides such
control in the form of subscriptions. Most servers support the control in the form of subscriptions. Most servers support the
SUBSCRIBE, UNSUBSCRIBE, and LSUB commands, and many users choose to SUBSCRIBE, UNSUBSCRIBE, and LSUB commands, and many users choose to
narrow down a large list of available mailboxes by subscribing to the narrow down a large list of available mailboxes by subscribing to the
ones that they usually want to see. Clients, with this in mind, ones that they usually want to see. Clients, with this in mind,
SHOULD give the user a way to see only subscribed mailboxes. A SHOULD give the user a way to see only subscribed mailboxes. A
client that never uses the LSUB command takes a significant usability client that never uses the LSUB command takes a significant usability
feature away from the user. Of course, the client would not want to feature away from the user. Of course, the client would not want to
hide the LIST command completely; the user needs to be able to go hide the LIST command completely; the user needs to have a way to
both ways. choose between LIST and LSUB. The usual way to do this is to provide
a setting like "show which mailboxes?: [] all [] subscribed only".
3.2.3. Searching 3.2.3. Searching
IMAP SEARCH commands can become particularly troublesome (that is, IMAP SEARCH commands can become particularly troublesome (that is,
slow) on mailboxes containing a large number of messages. So let's slow) on mailboxes containing a large number of messages. So let's
put a few things in perspective in that regard. put a few things in perspective in that regard.
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The flag searches SHOULD be fast. The flag searches (ALL, [UN]SEEN, The flag searches SHOULD be fast. The flag searches (ALL, [UN]SEEN,
[UN]ANSWERED, [UN]DELETED, [UN]DRAFT, [UN]FLAGGED, NEW, OLD, RECENT) [UN]ANSWERED, [UN]DELETED, [UN]DRAFT, [UN]FLAGGED, NEW, OLD, RECENT)
are known to be used by clients for the client's own use (for are known to be used by clients for the client's own use (for
instance, some clients use "SEARCH UNSEEN" to find unseen mail and instance, some clients use "SEARCH UNSEEN" to find unseen mail and
"SEARCH DELETED" to warn the user before expunging messages). "SEARCH DELETED" to warn the user before expunging messages).
Other searches, particularly the text searches (HEADER, TEXT, BODY) Other searches, particularly the text searches (HEADER, TEXT, BODY)
are initiated by the user, rather than by the client itself, and are initiated by the user, rather than by the client itself, and
somewhat slower performance can be tolerated, since the user is aware somewhat slower performance can be tolerated, since the user is aware
that the search is being done (and is probably aware that it might be that the search is being done (and is probably aware that it might be
time-consuming). time-consuming). A smart server might use dynamic indexing to speed
commonly used text searches.
The client MAY allow other commands to be sent to the server while a The client MAY allow other commands to be sent to the server while a
SEARCH is in progress, but at the time of this writing there is SEARCH is in progress, but at the time of this writing there is
little or no server support for parallel processing of multiple little or no server support for parallel processing of multiple
commands in the same session (and see "Multiple Accesses of the Same commands in the same session (and see "Multiple Accesses of the Same
Mailbox" above for a description of the dangers of trying to work Mailbox" above for a description of the dangers of trying to work
around this by doing your SEARCH in another session). around this by doing your SEARCH in another session).
Another word about text searches: some servers, built on database Another word about text searches: some servers, built on database
back-ends with indexed search capabilities, may return search results back-ends with indexed search capabilities, may return search results
that do not match the IMAP spec's "case-insensitive substring" that do not match the IMAP spec's "case-insensitive substring"
requirements. While these servers are in violation of the protocol, requirements. While these servers are in violation of the protocol,
there is little harm in the violation as long as the search results there is little harm in the violation as long as the search results
are used only to response to a user's request. Still, developers of are used only in response to a user's request. Still, developers of
such servers should be aware that they ARE violating the protocol, such servers should be aware that they ARE violating the protocol,
should think carefully about that behaviour, and MUST be certain that should think carefully about that behaviour, and MUST be certain that
their servers respond accurately to the flag searches for the reasons their servers respond accurately to the flag searches for the reasons
outlined above. outlined above.
In addition, servers SHOULD support CHARSET UTF-8 in searches. In addition, servers SHOULD support CHARSET UTF-8 [UTF-8] in
searches.
3.3 Avoiding Invalid Requests 3.3 Avoiding Invalid Requests
IMAP4 provides ways for a server to tell a client in advance what is IMAP4 provides ways for a server to tell a client in advance what is
and isn't permitted in some circumstances. Clients SHOULD use these and isn't permitted in some circumstances. Clients SHOULD use these
features to avoid sending requests that a well designed client would features to avoid sending requests that a well designed client would
know to be invalid. This section explains this in more detail. know to be invalid. This section explains this in more detail.
3.3.1. The CAPABILITY Command 3.3.1. The CAPABILITY Command
All IMAP4 clients SHOULD use the CAPABILITY command to determine what All IMAP4 clients SHOULD use the CAPABILITY command to determine what
version of IMAP and what optional features a server supports. The version of IMAP and what optional features a server supports. The
client SHOULD NOT send IMAP4rev1 commands and arguments to a server client SHOULD NOT send IMAP4rev1 commands and arguments to a server
that does not advertize IMAP4rev1 in its CAPABILITY response. that does not advertize IMAP4rev1 in its CAPABILITY response.
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Similarly, the client SHOULD NOT send IMAP4 commands that no longer Similarly, the client SHOULD NOT send IMAP4 commands that no longer
exist in IMAP4rev1 to a server that does not advertize IMAP4 in its exist in IMAP4rev1 to a server that does not advertize IMAP4 in its
CAPABILITY response. An IMAP4rev1 server is NOT required to support CAPABILITY response. An IMAP4rev1 server is NOT required to support
obsolete IMAP4 or IMAP2bis commands (though some do; do not let this obsolete IMAP4 or IMAP2bis commands (though some do; do not let this
fact lull you into thinking that it's valid to send such commands to fact lull you into thinking that it's valid to send such commands to
an IMAP4rev1 server). an IMAP4rev1 server).
A client SHOULD NOT send commands to probe for the existance of A client SHOULD NOT send commands to probe for the existance of
certain extensions. All standard and standards-track extensions certain extensions. All standard and standards-track extensions
include CAPABILITY tokens indicating their presense. All private and include CAPABILITY tokens indicating their presense. All private and
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section 2.2.2 and the preamble to section 7 of the IMAP4rev1 spec section 2.2.2 and the preamble to section 7 of the IMAP4rev1 spec
[RFC-2060]. [RFC-2060].
3.4.1. Well Formed Protocol 3.4.1. Well Formed Protocol
We cannot stress enough the importance of adhering strictly to the We cannot stress enough the importance of adhering strictly to the
protocol grammar. The specification of the protocol is quite rigid; protocol grammar. The specification of the protocol is quite rigid;
do not assume that you can insert blank space for "readability" if do not assume that you can insert blank space for "readability" if
none is called for. Keep in mind that there are parsers out there none is called for. Keep in mind that there are parsers out there
that will crash if there are protocol errors. There are clients that that will crash if there are protocol errors. There are clients that
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will report every parser burp to the user. And in any case, will report every parser burp to the user. And in any case,
information that cannot be parsed is information that is lost. Be information that cannot be parsed is information that is lost. Be
careful in your protocol generation. And see "A Word About Testing", careful in your protocol generation. And see "A Word About Testing",
below. below.
In particular, note that the string in the INTERNALDATE response is In particular, note that the string in the INTERNALDATE response is
NOT an RFC-822 date string - that is, it is not in the same format as NOT an RFC-822 date string - that is, it is not in the same format as
the first string in the ENVELOPE response. Since most clients will, the first string in the ENVELOPE response. Since most clients will,
in fact, accept an RFC-822 date string in the INTERNALDATE response, in fact, accept an RFC-822 date string in the INTERNALDATE response,
it's easy to miss this in your interoperability testing. But it will it's easy to miss this in your interoperability testing. But it will
cause a problem with some client, so be sure to generate the correct cause a problem with some client, so be sure to generate the correct
string for this field. string for this field.
3.4.2. Special Characters 3.4.2. Special Characters
Certain characters, currently the double-quote and the backslash, may Certain characters, currently the double-quote and the backslash, may
not be sent as-is inside a quoted string. These characters MUST be not be sent as-is inside a quoted string. These characters MUST be
preceded by the escape character if they are in a quoted string, or preceded by the escape character if they are in a quoted string, or
else the string must be sent as a literal. Both clients and servers else the string MUST be sent as a literal. Both clients and servers
MUST handle this, both on output (they must send these characters MUST handle this, both on output (they MUST send these characters
properly) and on input (they must be able to receive escaped properly) and on input (they MUST be able to receive escaped
characters in quoted strings). Example: characters in quoted strings). Example:
C: 001 LIST "" % C: 001 LIST "" %
S: * LIST () "" INBOX S: * LIST () "" INBOX
S: * LIST () "\\" TEST S: * LIST () "\\" TEST
S: * LIST () "\\" {12} S: * LIST () "\\" {12}
S: "My" mailbox S: "My" mailbox
S: 001 OK done S: 001 OK done
C: 002 LIST "" "\"My\" mailbox\\%" C: 002 LIST "" "\"My\" mailbox\\%"
S: * LIST () "\\" {17} S: * LIST () "\\" {17}
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an escaped character in the quoted string and sent the mailbox name an escaped character in the quoted string and sent the mailbox name
containing imbedded double-quotes as a literal. The client used only containing imbedded double-quotes as a literal. The client used only
quoted strings, escaping both the backslash and the double-quote quoted strings, escaping both the backslash and the double-quote
characters. characters.
The CR and LF characters may be sent ONLY in literals; they are not The CR and LF characters may be sent ONLY in literals; they are not
allowed, even if escaped, inside quoted strings. allowed, even if escaped, inside quoted strings.
And while we're talking about special characters: the IMAP spec, in And while we're talking about special characters: the IMAP spec, in
the section titled "Mailbox International Naming Convention", the section titled "Mailbox International Naming Convention",
describes how to encode mailbox names in modified UTF-7. describes how to encode mailbox names in modified UTF-7 [UTF-7 and
Implementations MUST adhere to this in order to be interoperable in RFC-2060]. Implementations MUST adhere to this in order to be
the international market, and servers SHOULD validate mailbox names interoperable in the international market, and servers SHOULD
sent by client and reject names that do not conform.
Internet DRAFT Implementation Recommendations December 1998
validate mailbox names sent by client and reject names that do not
conform.
3.4.3. UIDs and UIDVALIDITY 3.4.3. UIDs and UIDVALIDITY
Servers that support existing back-end mail stores often have no good Servers that support existing back-end mail stores often have no good
place to save UIDs for messages. Often the existing mail store will place to save UIDs for messages. Often the existing mail store will
not have the concept of UIDs in the sense that IMAP has: strictly not have the concept of UIDs in the sense that IMAP has: strictly
increasing, never re-issued, 32-bit integers. Some servers solve increasing, never re-issued, 32-bit integers. Some servers solve
this by storing the UIDs in a place that's accessible to end users, this by storing the UIDs in a place that's accessible to end users,
allowing for the possibility that the users will delete them. Others allowing for the possibility that the users will delete them. Others
solve it by re-assigning UIDs every time a mailbox is selected. solve it by re-assigning UIDs every time a mailbox is selected.
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The server SHOULD maintain UIDs permanently for all messages if it The server SHOULD maintain UIDs permanently for all messages if it
can. If that's not possible, the server MUST change the UIDVALIDITY can. If that's not possible, the server MUST change the UIDVALIDITY
value for the mailbox whenever any of the UIDs may have become value for the mailbox whenever any of the UIDs may have become
invalid. Clients MUST recognize that the UIDVALIDITY has changed and invalid. Clients MUST recognize that the UIDVALIDITY has changed and
MUST respond to that condition by throwing away any information that MUST respond to that condition by throwing away any information that
they have saved about UIDs in that mailbox. There have been many they have saved about UIDs in that mailbox. There have been many
problems in this area when clients have failed to do this; in the problems in this area when clients have failed to do this; in the
worst case it will result in loss of mail when a client deletes the worst case it will result in loss of mail when a client deletes the
wrong piece of mail by using a stale UID. wrong piece of mail by using a stale UID.
It seems to be a common myth that "the UIDVALIDITY and the UID, taken It seems to be a common misunderstanding that "the UIDVALIDITY and
together, form a 64-bit identifier that uniquely identifies a message the UID, taken together, form a 64-bit identifier that uniquely
on a server". This is absolutely NOT TRUE. There is no assurance identifies a message on a server". This is absolutely NOT TRUE.
that the UIDVALIDITY values of two mailboxes be different, so the There is no assurance that the UIDVALIDITY values of two mailboxes be
UIDVALIDITY in no way identifies a mailbox. The ONLY purpose of different, so the UIDVALIDITY in no way identifies a mailbox. The
UIDVALIDITY is, as its name indicates, to give the client a way to ONLY purpose of UIDVALIDITY is, as its name indicates, to give the
check the validity of the UIDs it has cached. While it is a valid client a way to check the validity of the UIDs it has cached. While
implementation choice to put these values together to make a 64-bit it is a valid implementation choice to put these values together to
identifier for the message, the important concept here is that UIDs make a 64-bit identifier for the message, the important concept here
are not unique between mailboxes; they are only unique WITHIN a given is that UIDs are not unique between mailboxes; they are only unique
mailbox. WITHIN a given mailbox.
Some server implementations have toyed with making UIDs unique across Some server implementations have attempted to make UIDs unique across
the entire server. This is inadvisable, in that it limits the life the entire server. This is inadvisable, in that it limits the life
of UIDs unnecessarily. The UID is a 32-bit number and will run out of UIDs unnecessarily. The UID is a 32-bit number and will run out
in reasonably finite time if it's global across the server. If you in reasonably finite time if it's global across the server. If you
assign UIDs sequentially in one mailbox, you will not have to start assign UIDs sequentially in one mailbox, you will not have to start
re-using them until you have had, at one time or another, 2**32 re-using them until you have had, at one time or another, 2**32
different messages in that mailbox. In the global case, you will different messages in that mailbox. In the global case, you will
have to reuse them once you have had, at one time or another, 2**32 have to reuse them once you have had, at one time or another, 2**32
different messages in the entire mail store. Suppose your server has different messages in the entire mail store. Suppose your server has
around 8000 users registered (2**13). That gives an average of 2**19 around 8000 users registered (2**13). That gives an average of 2**19
UIDs per user. Suppose each user gets 32 messages (2**5) per day. UIDs per user. Suppose each user gets 32 messages (2**5) per day.
That gives you 2**14 days (16000+ days = about 45 years) before you That gives you 2**14 days (16000+ days = about 45 years) before you
run out. That may seem like enough, but multiply the usage just a run out. That may seem like enough, but multiply the usage just a
Internet DRAFT Implementation Recommendations December 1998
little (a lot of spam, a lot of mailing list subscriptions, more little (a lot of spam, a lot of mailing list subscriptions, more
users) and you limit yourself too much. users) and you limit yourself too much.
What's worse is that if you have to wrap the UIDs, and, thus, you What's worse is that if you have to wrap the UIDs, and, thus, you
have to change UIDVALIDITY and invalidate the UIDs in the mailbox, have to change UIDVALIDITY and invalidate the UIDs in the mailbox,
you have to do it for EVERY mailbox in the system, since they all you have to do it for EVERY mailbox in the system, since they all
share the same UID pool. If you assign UIDs per mailbox and you have share the same UID pool. If you assign UIDs per mailbox and you have
a problem, you only have to kill the UIDs for that one mailbox. a problem, you only have to kill the UIDs for that one mailbox.
Under extreme circumstances (and this is extreme, indeed), the server Under extreme circumstances (and this is extreme, indeed), the server
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that is, the UIDs that the client knows about in its active mailbox that is, the UIDs that the client knows about in its active mailbox
are no longer valid. In that case, the server MUST immediately are no longer valid. In that case, the server MUST immediately
change the UIDVALIDITY and MUST communicate this to the client. The change the UIDVALIDITY and MUST communicate this to the client. The
server MAY do this by sending an unsolicited UIDVALIDITY message, in server MAY do this by sending an unsolicited UIDVALIDITY message, in
the same form as in response to the SELECT command. Clients MUST be the same form as in response to the SELECT command. Clients MUST be
prepared to handle such a message and the possibly coincident failure prepared to handle such a message and the possibly coincident failure
of the command in process. For example: of the command in process. For example:
C: 032 UID STORE 382 +Flags.silent \Deleted C: 032 UID STORE 382 +Flags.silent \Deleted
S: * OK [UIDVALIDITY 12345] New UIDVALIDITY value! S: * OK [UIDVALIDITY 12345] New UIDVALIDITY value!
S: 032 NO UID command rejeced because UIDVALIDITY changed! S: 032 NO UID command rejected because UIDVALIDITY changed!
C: ...invalidates local information and re-fetches... C: ...invalidates local information and re-fetches...
C: 033 FETCH 1:* UID C: 033 FETCH 1:* UID
...etc... ...etc...
At the time of the writing of this document, the only server known to At the time of the writing of this document, the only server known to
do this does so only under the following condition: the client do this does so only under the following condition: the client
selects INBOX, but there is not yet a physical INBOX file created. selects INBOX, but there is not yet a physical INBOX file created.
Nonetheless, the SELECT succeeds, exporting an empty INBOX with a Nonetheless, the SELECT succeeds, exporting an empty INBOX with a
temporary UIDVALIDITY of 1. While the INBOX remains selected, mail temporary UIDVALIDITY of 1. While the INBOX remains selected, mail
is delivered to the user, which creates the real INBOX file and is delivered to the user, which creates the real INBOX file and
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Alternatively, a server may force the client to re-select the Alternatively, a server may force the client to re-select the
mailbox, at which time it will obtain a new UIDVALIDITY value. To do mailbox, at which time it will obtain a new UIDVALIDITY value. To do
this, the server closes this client session (see "Severed this, the server closes this client session (see "Severed
Connections" above) and the client then reconnects and gets back in Connections" above) and the client then reconnects and gets back in
synch. Clients MUST be prepared for either of these behaviours. synch. Clients MUST be prepared for either of these behaviours.
We do not know of, nor do we anticipate the future existance of, a We do not know of, nor do we anticipate the future existance of, a
server that changes UIDVALIDITY while there are existing messages, server that changes UIDVALIDITY while there are existing messages,
but clients MUST be prepared to handle this eventuality. but clients MUST be prepared to handle this eventuality.
Internet DRAFT Implementation Recommendations December 1998
3.4.4. FETCH Responses 3.4.4. FETCH Responses
When a client asks for certain information in a FETCH command, the When a client asks for certain information in a FETCH command, the
server MAY return the requested information in any order, not server MAY return the requested information in any order, not
necessarily in the order that it was requested. Further, the server necessarily in the order that it was requested. Further, the server
MAY return the information in separate FETCH responses and MAY also MAY return the information in separate FETCH responses and MAY also
return information that was not explicitly requested (to reflect to return information that was not explicitly requested (to reflect to
the client changes in the state of the subject message). Some the client changes in the state of the subject message). Some
examples: examples:
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in any particular order, or even that any will come at all. If after in any particular order, or even that any will come at all. If after
receiving the tagged response for a FETCH command the client finds receiving the tagged response for a FETCH command the client finds
that it did not get all of the information requested, the client that it did not get all of the information requested, the client
SHOULD send a NOOP command to the server to ensure that the server SHOULD send a NOOP command to the server to ensure that the server
has an opportunity to send any pending EXPUNGE responses to the has an opportunity to send any pending EXPUNGE responses to the
client (see [RFC-2180]). client (see [RFC-2180]).
3.4.5. RFC822.SIZE 3.4.5. RFC822.SIZE
Some back-end mail stores keep the mail in a canonical form, rather Some back-end mail stores keep the mail in a canonical form, rather
Internet DRAFT Implementation Recommendations December 1998
than retaining the original MIME format of the messages. This means than retaining the original MIME format of the messages. This means
that the server must reassemble the message to produce a MIME stream that the server must reassemble the message to produce a MIME stream
when a client does a fetch such as RFC822 or BODY[], requesting the when a client does a fetch such as RFC822 or BODY[], requesting the
entire message. It also may mean that the server has no convenient entire message. It also may mean that the server has no convenient
way to know the RFC822.SIZE of the message. Often, such a server way to know the RFC822.SIZE of the message. Often, such a server
will actually have to build the MIME stream to compute the size, only will actually have to build the MIME stream to compute the size, only
to throw the stream away and report the size to the client. to throw the stream away and report the size to the client.
When this is the case, some servers have chosen to estimate the size, When this is the case, some servers have chosen to estimate the size,
rather than to compute it precisely. Such an estimate allows the rather than to compute it precisely. Such an estimate allows the
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explanation and for recommendations. explanation and for recommendations.
3.4.7. The Namespace Issue 3.4.7. The Namespace Issue
Namespaces are a very muddy area in IMAP4 implementation right now Namespaces are a very muddy area in IMAP4 implementation right now
(see [NAMESPACE] for a proposal to clear the water a bit). Until the (see [NAMESPACE] for a proposal to clear the water a bit). Until the
issue is resolved, the important thing for client developers to issue is resolved, the important thing for client developers to
understand is that some servers provide access through IMAP to more understand is that some servers provide access through IMAP to more
than just the user's personal mailboxes, and, in fact, the user's than just the user's personal mailboxes, and, in fact, the user's
personal mailboxes may be "hidden" somewhere in the user's default personal mailboxes may be "hidden" somewhere in the user's default
Internet DRAFT Implementation Recommendations December 1998
hierarchy. The client, therefore, SHOULD provide a setting wherein hierarchy. The client, therefore, SHOULD provide a setting wherein
the user can specify a prefix to be used when accessing mailboxes. the user can specify a prefix to be used when accessing mailboxes.
If the user's mailboxes are all in "~/mail/", for instance, then the If the user's mailboxes are all in "~/mail/", for instance, then the
user can put that string in the prefix. The client would then put user can put that string in the prefix. The client would then put
the prefix in front of any name pattern in the LIST and LSUB the prefix in front of any name pattern in the LIST and LSUB
commands: commands:
C: 001 LIST "" ~/mail/% C: 001 LIST "" ~/mail/%
(See also "Reference Names in the LIST Command" below.) (See also "Reference Names in the LIST Command" below.)
3.4.8. Creating Special-Use Mailboxes 3.4.8. Creating Special-Use Mailboxes
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The client developer is, therefore, well advised to consider The client developer is, therefore, well advised to consider
carefully the creation of any special-use mailboxes on the server, carefully the creation of any special-use mailboxes on the server,
and, further, the client MUST NOT require such mailbox creation - and, further, the client MUST NOT require such mailbox creation -
that is, if you do decide to do this, you MUST handle gracefully the that is, if you do decide to do this, you MUST handle gracefully the
failure of the CREATE command and behave reasonably when your failure of the CREATE command and behave reasonably when your
special-use mailboxes do not exist and can not be created. special-use mailboxes do not exist and can not be created.
In addition, the client developer SHOULD provide a convenient way for In addition, the client developer SHOULD provide a convenient way for
the user to select the names for any special-use mailboxes, allowing the user to select the names for any special-use mailboxes, allowing
the user to make these names the same in all clients s/he uses and to the user to make these names the same in all clients used and to put
put them where s/he wants them. them where the user wants them.
3.4.9. Reference Names in the LIST Command 3.4.9. Reference Names in the LIST Command
Many implementers of both clients and servers are confused by the Many implementers of both clients and servers are confused by the
"reference name" on the LIST command. The reference name is intended "reference name" on the LIST command. The reference name is intended
to be used in much the way a "cd" (change directory) command is used to be used in much the way a "cd" (change directory) command is used
on Unix, PC DOS, Windows, and OS/2 systems. That is, the mailbox on Unix, PC DOS, Windows, and OS/2 systems. That is, the mailbox
name is interpreted in much the same way as a file of that name would name is interpreted in much the same way as a file of that name would
be found if one had done a "cd" command into the directory specified be found if one had done a "cd" command into the directory specified
by the reference name. For example, in Unix we have the following: by the reference name. For example, in Unix we have the following:
Internet DRAFT Implementation Recommendations December 1998
> cd /u/jones/junk > cd /u/jones/junk
> vi banana [file is "/u/jones/junk/banana"] > vi banana [file is "/u/jones/junk/banana"]
> vi stuff/banana [file is "/u/jones/junk/stuff/banana"] > vi stuff/banana [file is "/u/jones/junk/stuff/banana"]
> vi /etc/hosts [file is "/etc/hosts"] > vi /etc/hosts [file is "/etc/hosts"]
The interoperability problems with this, in practice, are several. The interoperability problems with this, in practice, are several.
First, while some IMAP servers are built on Unix or PC file systems, First, while some IMAP servers are built on Unix or PC file systems,
many others are not, and the file system semantics do not make sense many others are not, and the file system semantics do not make sense
in those configurations. Second, while some IMAP servers expose the in those configurations. Second, while some IMAP servers expose the
underlying file system to the clients, others allow access only to underlying file system to the clients, others allow access only to
the user's personal mailboxes, or to some other limited set of files, the user's personal mailboxes, or to some other limited set of files,
making such file-system-like semantics less meaningful. Third, making such file-system-like semantics less meaningful. Third,
because the IMAP spec leaves the interpretation of the reference name because the IMAP spec leaves the interpretation of the reference name
as "implementation-dependent", the various server implementations as "implementation-dependent", the various server implementations
handle it in vastly differing ways, and fourth, many implementers handle it in vastly differing ways, and fourth, many implementers
simply do not understand it and misuse it, do not use it, or ignore simply do not understand it and misuse it, do not use it, or ignore
it as a result. it as a result.
The following statement gets somewhat into the religious issues that The following statement gets somewhat into the religious issues that
we've tried to avoid scrupulously here; so be it: because of the we've tried to avoid scrupulously here: because of the confusion
confusion around the reference name, its use by a client is a around the reference name, its use by a client is a dangerous thing,
dangerous thing, prone to result in interoperability problems. There prone to result in interoperability problems. There are servers that
are servers that interpret it as originally intended; there are interpret it as originally intended; there are servers that ignore it
servers that ignore it completely; there are servers that simply completely; there are servers that simply prepend it to the mailbox
prepend it to the mailbox name (with or without inserting a hierarchy name (with or without inserting a hierarchy delimiter in between).
delimiter in between). Because a client can't know which of these Because a client can't know which of these four behaviours to expect,
four behaviours to expect, a client SHOULD NOT use a reference name a client SHOULD NOT use a reference name itself, expecting a
itself, expecting a particular server behavior. However, a client particular server behavior. However, a client SHOULD permit a USER,
SHOULD permit a USER, by configuration, to use a reference name. by configuration, to use a reference name.
There is in no way universal agreement about the use or non-use of There is in no way universal agreement about the use or non-use of
the reference name. The last words here are, "Be aware." the reference name. The last words here are, "Be aware."
3.4.12. Mailbox Hierarchy Delimiters 3.4.12. Mailbox Hierarchy Delimiters
The server's selection of what to use as a mailbox hierarchy The server's selection of what to use as a mailbox hierarchy
delimiter is a difficult one, involving several issues: What delimiter is a difficult one, involving several issues: What
characters do users expect to see? What characters can they enter characters do users expect to see? What characters can they enter
for a hierarchy delimiter if it is desired (or required) that the for a hierarchy delimiter if it is desired (or required) that the
user enter it? What character can be used for the hierarchy user enter it? What character can be used for the hierarchy
delimiter, nothing that the chosen character can not otherwise be delimiter, noting that the chosen character can not otherwise be used
used in the mailbox name? in the mailbox name?
Because some interfaces show users the hierarchy delimiters or allow Because some interfaces show users the hierarchy delimiters or allow
users to enter qualified mailbox names containing them, server users to enter qualified mailbox names containing them, server
implementations SHOULD use delimiter characters that users generally implementations SHOULD use delimiter characters that users generally
expect to see as name separators. The most common characters used expect to see as name separators. The most common characters used
Internet DRAFT Implementation Recommendations December 1998
for this are "/" (as in Unix file names), "\" (as in OS/2 and Windows for this are "/" (as in Unix file names), "\" (as in OS/2 and Windows
file names), and "." (as in news groups). There is little to choose file names), and "." (as in news groups). There is little to choose
among these apart from what users may expect or what is dictated by among these apart from what users may expect or what is dictated by
the underlying file system, if any. One consideration about using the underlying file system, if any. One consideration about using
"\" is that it's also a special character in the IMAP protocol. "\" is that it's also a special character in the IMAP protocol.
While the use of other hierarchy delimiter characters is permissible, While the use of other hierarchy delimiter characters is permissible,
A DESIGNER IS WELL ADVISED TO STAY WITH ONE FROM THIS SET unless the A DESIGNER IS WELL ADVISED TO STAY WITH ONE FROM THIS SET unless the
server is intended for special purposes only. Implementers might be server is intended for special purposes only. Implementers might be
thinking about using characters such as "-", "_", ";", "&", "#", "@", thinking about using characters such as "-", "_", ";", "&", "#", "@",
and "!", but they should be aware of the surprise to the user as well and "!", but they should be aware of the surprise to the user as well
as of the effect on URLs and other external specifications (since as of the effect on URLs and other external specifications (since
some of these characters have special meanings there). Also, a some of these characters have special meanings there). Also, a
server that uses "\" (and clients of such a server) must remember to server that uses "\" (and clients of such a server) MUST remember to
escape that character in quoted strings or to send literals instead. escape that character in quoted strings or to send literals instead.
Literals are recommended over escaped characters in quoted strings in Literals are recommended over escaped characters in quoted strings in
order to maintain compatibility with older IMAP versions that did not order to maintain compatibility with older IMAP versions that did not
allow escaped characters in quoted strings (but check the grammar to allow escaped characters in quoted strings (but check the grammar to
see where literals are allowed): see where literals are allowed):
C: 001 LIST "" {13} C: 001 LIST "" {13}
S: + send literal S: + send literal
C: this\%\%\%\h* C: this\%\%\%\h*
S: * LIST () "\\" {27} S: * LIST () "\\" {27}
S: this\is\a\mailbox\hierarchy S: this\is\a\mailbox\hierarchy
S: 001 OK LIST complete S: 001 OK LIST complete
In any case, a server SHOULD NOT use normal alpha-numeric characters In any case, a server SHOULD NOT use normal alpha-numeric characters
(such as "X" or "0") as delimiters; a user would be very surprised to (such as "X" or "0") as delimiters; a user would be very surprised to
find that "EXPENDITURES" actually represented a two-level hierarchy. find that "EXPENDITURES" actually represented a two-level hierarchy.
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alphabets fit into this category. Their use presents alphabets fit into this category. Their use presents
interoperability problems that are best avoided. interoperability problems that are best avoided.
The UTF-7 encoding of mailbox names also raises questions about what The UTF-7 encoding of mailbox names also raises questions about what
to do with the hierarchy delimiters in encoded names: do we encode to do with the hierarchy delimiters in encoded names: do we encode
each hierarchy level and separate them with delimiters, or do we each hierarchy level and separate them with delimiters, or do we
encode the fully qualified name, delimiters and all? The answer for encode the fully qualified name, delimiters and all? The answer for
IMAP is the former: encode each hierarchy level separately, and IMAP is the former: encode each hierarchy level separately, and
insert delimiters between. This makes it particularly important not insert delimiters between. This makes it particularly important not
to use as a hierarchy delimiter a character that might cause to use as a hierarchy delimiter a character that might cause
confusion with IMAP's modified UTF-7 encoding. confusion with IMAP's modified UTF-7 [UTF-7 and RFC-2060] encoding.
To repeat: a server SHOULD use "/", "\", or "." as its hierarchy To repeat: a server SHOULD use "/", "\", or "." as its hierarchy
delimiter. The use of any other character is likely to cause delimiter. The use of any other character is likely to cause
problems and is STRONGLY DISCOURAGED. problems and is STRONGLY DISCOURAGED.
Internet DRAFT Implementation Recommendations December 1998
3.4.11. ALERT Response Codes 3.4.11. ALERT Response Codes
The protocol spec is very clear on the matter of what to do with The protocol spec is very clear on the matter of what to do with
ALERT response codes, and yet there are many clients that violate it ALERT response codes, and yet there are many clients that violate it
so it needs to be said anyway: "The human-readable text contains a so it needs to be said anyway: "The human-readable text contains a
special alert that MUST be presented to the user in a fashion that special alert that MUST be presented to the user in a fashion that
calls the user's attention to the message." Enough said. Do it. calls the user's attention to the message." That should be clear
enough, but I'll repeat it here: Clients MUST present ALERT text
clearly to the user.
3.4.12. Deleting Mailboxes 3.4.12. Deleting Mailboxes
The protocol does not guarantee that a client may delete a mailbox The protocol does not guarantee that a client may delete a mailbox
that is not empty, though on some servers it is permissible and is, that is not empty, though on some servers it is permissible and is,
in fact, much faster than the alternative or deleting all the in fact, much faster than the alternative or deleting all the
messages from the client. If the client chooses to try to take messages from the client. If the client chooses to try to take
advantage of this possibility it MUST be prepared to use the other advantage of this possibility it MUST be prepared to use the other
method in the even that the more convenient one fails. Further, a method in the even that the more convenient one fails. Further, a
client SHOULD NOT try to delete the mailbox that it has selected, but client SHOULD NOT try to delete the mailbox that it has selected, but
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C: 010 SELECT BANANA C: 010 SELECT BANANA
S: * ... untagged SELECT responses S: * ... untagged SELECT responses
S: 010 OK done S: 010 OK done
C: 011 STORE 1:* +FLAGS.SILENT \DELETED C: 011 STORE 1:* +FLAGS.SILENT \DELETED
S: 011 OK done S: 011 OK done
C: 012 CLOSE C: 012 CLOSE
S: 012 OK done S: 012 OK done
C: 013 DELETE BANANA C: 013 DELETE BANANA
S: 013 OK done S: 013 OK done
Internet DRAFT Implementation Recommendations December 1998
3.5. A Word About Testing 3.5. A Word About Testing
Since the whole point of IMAP is interoperability, and since Since the whole point of IMAP is interoperability, and since
interoperability can not be tested in a vacuum, the final interoperability can not be tested in a vacuum, the final
recommendation of this treatise is, "Test against EVERYTHING." Test recommendation of this treatise is, "Test against EVERYTHING." Test
your client against every server you can get an account on. Test your client against every server you can get an account on. Test
your server with every client you can get your hands on. Many your server with every client you can get your hands on. Many
clients make limited test versions available on the Web for the clients make limited test versions available on the Web for the
downloading. Many server owners will give serious client developers downloading. Many server owners will give serious client developers
guest accounts for testing. Contact them and ask. NEVER assume that guest accounts for testing. Contact them and ask. NEVER assume that
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IMC MailConnect: http://www.imc.org/imc-mailconnect IMC MailConnect: http://www.imc.org/imc-mailconnect
4. Security Considerations 4. Security Considerations
This document describes behaviour of clients and servers that use the This document describes behaviour of clients and servers that use the
IMAP4 protocol, and as such, has the same security considerations as IMAP4 protocol, and as such, has the same security considerations as
described in [RFC-2060]. described in [RFC-2060].
5. References 5. References
[RFC-2060], Crispin, M., "Internet Message Access Protocol - Version [RFC-2060]; Crispin, M.; "Internet Message Access Protocol - Version
4rev1", RFC 2060, University of Washington, December 1996. 4rev1"; RFC 2060; University of Washington; December 1996.
[RFC-2119], Bradner, S., "Key words for use in RFCs to Indicate [RFC-2119]; Bradner, S.; "Key words for use in RFCs to Indicate
Requirement Levels", RFC 2119, Harvard University, March 1997. Requirement Levels"; RFC 2119; Harvard University; March 1997.
[RFC-2180], Gahrns, M., "IMAP4 Multi-Accessed Mailbox Practice", RFC [RFC-2180]; Gahrns, M.; "IMAP4 Multi-Accessed Mailbox Practice"; RFC
2180, Microsoft, July 1997. 2180; Microsoft; July 1997.
[NAMESPACE], Gahrns, M. & Newman, C., "IMAP4 Namespace", draft [UTF-8]; Yergeau, F.; " UTF-8, a transformation format of Unicode and
document <draft-gahrns-imap-namespace-01.txt>, June 1997. ISO 10646"; RFC 2044; Alis Technilogies; October 1996.
[UTF-7]; Goldsmith, D. & Davis, M.; "UTF-7, a Mail-Safe
Transformation Format of Unicode"; RFC 2152; Apple Computer, Inc. &
Taligent, Inc.; May 1997.
[NAMESPACE]; Gahrns, M. & Newman, C.; "IMAP4 Namespace"; draft
Internet DRAFT Implementation Recommendations December 1998
document <draft-gahrns-imap-namespace-01.txt>; Microsoft & Innosoft;
June 1997.
6. Author's Address 6. Author's Address
Barry Leiba Barry Leiba
IBM T.J. Watson Research Center IBM T.J. Watson Research Center
30 Saw Mill River Road 30 Saw Mill River Road
Hawthorne, NY 10532 Hawthorne, NY 10532
Phone: 1-914-784-7941 Phone: 1-914-784-7941
Email: leiba@watson.ibm.com Email: leiba@watson.ibm.com
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