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2 Network Working Group A. Hathcock
3 Internet-Draft J. Merkel
4 Intended Status: Informational Alt-N Technologies
5 Expires: September 6, 2007 March 6, 2007
7 The Minger Email Address Verification Protocol
8 draft-hathcock-minger-00.txt
10 Status of this Memo
12 By submitting this Internet-Draft, each author represents that any
13 applicable patent or other IPR claims of which he or she is aware
14 have been or will be disclosed, and any of which he or she becomes
15 aware will be disclosed, in accordance with Section 6 of BCP 79.
17 Internet-Drafts are working documents of the Internet Engineering
18 Task Force (IETF), its areas, and its working groups. Note that
19 other groups may also distribute working documents as Internet-
20 Drafts.
22 Internet-Drafts are draft documents valid for a maximum of six months
23 and may be updated, replaced, or obsoleted by other documents at any
24 time. It is inappropriate to use Internet-Drafts as reference
25 material or to cite them other than as "work in progress."
27 The list of current Internet-Drafts can be accessed at
28 http://www.ietf.org/ietf/1id-abstracts.txt.
30 The list of Internet-Draft Shadow Directories can be accessed at
31 http://www.ietf.org/shadow.html.
33 This Internet-Draft will expire on September 6, 2007.
35 Copyright Notice
37 Copyright (C) The IETF Trust (2007).
39 Abstract
41 This document describes the Minger protocol. Minger is a protocol
42 for determining whether an email address exists and, optionally,
43 retrieving some basic information about the user of that address.
44 It includes security in the form of a username/password combination
45 but can also be used anonymously if desired.
47 Requirements Language
49 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
50 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
51 document are to be interpreted as described in [RFC2119].
53 Table of Contents
55 1 Introduction . . . . . . . . . . . . . . . . . . . . . . . 3
56 1.1 The problem . . . . . . . . . . . . . . . . . . . . . . . 3
57 1.2 Existing solutions . . . . . . . . . . . . . . . . . . . . 3
58 1.2.1 Finger . . . . . . . . . . . . . . . . . . . . . . . . . . 3
59 1.2.2 SMTP "call-back" / "call-forward" . . . . . . . . . . . . 3
60 1.3 The solution . . . . . . . . . . . . . . . . . . . . . . . 4
61 2. The Minger protocol . . . . . . . . . . . . . . . . . . . 4
62 2.1 The Minger query process . . . . . . . . . . . . . . . . . 4
63 2.2 Minger responses . . . . . . . . . . . . . . . . . . . . . 5
64 2.2.1 Example responses . . . . . . . . . . . . . . . . . . . . 5
65 3. Anonymous mode . . . . . . . . . . . . . . . . . . . . . . 6
66 4. Security Considerations . . . . . . . . . . . . . . . . . 7
67 5. IANA Considerations . . . . . . . . . . . . . . . . . . . 7
68 6. Informative References . . . . . . . . . . . . . . . . . . 8
70 Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 9
71 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 9
72 Intellectual Property and Copyright Statements . . . . . . . . . . 10
74 1. Introduction
76 1.1 The problem
78 It is common for elements within a typical email handling topology
79 to be unaware of whether individual local-parts are valid for the
80 mail it accepts. For example, so-called "edge" servers which provide
81 security oriented services for downstream mail handling elements
82 often do not have an exhaustive listing of all valid local-parts for
83 a given domain. Thus, they are sometimes forced to accept messages
84 which might otherwise be rejected as "user unknown". Similarly,
85 entities offering "backup MX" mail services are rarely privy to a
86 complete local-part listing and are therefore forced to accept
87 messages which might otherwise be rejected. Finally, even within a
88 common administrative framework of several locally maintained and
89 controlled SMTP servers in a load balanced configuration, it is not
90 always possible for all servers to access a common local-part
91 database.
93 1.2 Existing solutions
95 The need to determine whether an email address contains a valid local
96 part has lead to the use of at least two existing mechanisms - Finger
97 [RFC1288] and SMTP "call-back" / "call-forward".
99 1.2.1 Finger
101 Finger [RFC1288] describes a protocol for the exchange of user
102 information. In theory, Finger could be used to determine whether an
103 account exists by careful examination of the results of a Finger
104 query. However, Finger suffers from a lack of security which makes
105 its modern day use problematic. For example, it is possible for
106 attackers to obtain information about the users of an email system
107 which they can then sell or use as targets for spam and viruses.
108 Also, Finger requires the use of TCP rather than UDP which seems ill
109 suited to a simple verification scheme.
111 1.2.2 SMTP "call-back" / "call-forward"
113 These terms are used to describe a widespread practice whereby SMTP
114 servers place an incoming SMTP session on hold while they attempt to
115 use an outbound SMTP session to determine whether or not a given
116 email address is valid. The theory behind this is as follows: if an
117 SMTP server responds positively to an SMTP RCPT or MAIL command
118 [RFC2821] with a given email address then this potentially means that
119 the address local part is valid. One problem with such a scheme is
120 the lack of efficiency inherent in the need to tear-up and tear-down
121 an SMTP session over TCP. Also, because these types of SMTP sessions
122 are not purposed to deliver mail, they typically drop connection
123 after the RCPT command is processed. This leads to a large number of
124 SMTP sessions which appear in logs to have simply failed for no
125 reason.
127 1.3 The solution
129 What's needed is a UDP based protocol which is secure, has little
130 overhead, and can be easily invoked to determine whether a given
131 email address is valid or not. Minger fulfills this need.
133 2. The Minger protocol
135 Minger is a UDP protocol that operates on port 49152.
137 Editor's note: The authors have applied to IANA for a
138 registered port. Until then, implementations will test
139 using the above private port.
141 Syntax descriptions use the form described in Augmented Backus-Naur
142 Form for Syntax Specifications (ABNF) [RFC4234].
144 2.1 The Minger query process
146 A Minger client constructs a query string comprised of either two or
147 four elements and transmits it over UDP to a Minger server. The
148 format of the query is as follows:
150 ABNF:
152 Query string = id SP mailbox [SP username SP password]
154 id = 1 * 50(VCHAR) ; used to match a query to a
155 ; response
157 mailbox = Local-part "@" Domain ; as defined in RFC2821
159 username = 1 * 50(VCHAR) ; optional username for security
161 password = 1 * 50(VCHAR) ; optional password for security
163 id - This is a randomly generated value which Minger clients include
164 in each query. This same value will be echoed back in the
165 response returned by the Minger server and can therefore be used
166 to match responses with the proper query.
168 mailbox - This is the email address for which verification of
169 existence is desired.
171 username and password - These values are pre-arranged elements
172 determined and configured in advance so that Minger servers
173 provide service only to authorized clients. When not provided,
174 Minger is operating in anonymous mode.
176 2.2 Minger responses
178 Minger servers return responses in a simple XML format. Despite the
179 overhead of including XML tags within the limited space available
180 with UDP, XML allows for very easy parsing by the receiving client
181 and the data returned would rarely approach the UDP space limit. The
182 XML format returned by the Minger server has certain required
183 elements but can include other elements as desired by particular
184 implementations.
186 ABNF:
188 Response = "" minger-data ""
190 Minger-data = "" id "" (status user-data / error)
192 id = 1 * 50(VCHAR) ; id of the query being responded to
194 status = "" ("Active" / "Not found" / "Disabled" /
195 1*(ALPHA / DIGIT)) ""
197 error = "" 1 * (ALPHA / DIGIT) ""
199 user-data = *("<" tag-name ">" 1 * (VCHAR) "" tag-name ">")
201 tag-name = 1 * (VCHAR)
203 Minger servers MUST support "status" values of "active", "not found",
204 and "disabled".
206 Minger servers MAY return additional XML nodes containing data not
207 defined in this specification.
209 2.2.1 Example responses
211 A. Minger response when email address "not found" (returned when the
212 queried email address does not exist):
214
215 12345
216 not found
217
219 B. Minger response for error conditions (in this case, invalid
220 credentials):
222
223 54321
224 bad username or password
225
227 C. Minger response for "active" email addresses (returned when the
228 queried email address exists and is ready to receive mail):
230
231 abc123def
232 Active
233
235 D. Minger response returning optional extra data:
237
238 gfs54ad4fs
239 Active
240 Arvel Hathcock
241 arvel@altn.com
242
244 3. Anonymous mode
246 Minger clients MAY attempt anonymous queries; that is, queries which
247 do not contain a username or password within the query string.
248 Minger servers SHOULD respond to anonymous queries in the same way
249 they respond to authenticated queries. However, Minger servers MAY
250 be configured to refuse anonymous queries. If so, they MUST respond
251 with an error as described above. Additionally, Minger responses to
252 anonymous queries may contain a sub-set or none of the optional extra
253 XML data that would otherwise be present. However, any response must
254 meet the minimums required by this specification.
256 4. Security Considerations
258 Minger is used to obtain information about the validity of an email
259 address. It can also be used to retrieve implementation specific
260 "extra" data about the user of an email address. Minger include a
261 username/password concept to prevent unauthorized use. However, it
262 also supports an anonymous mode in which use of these credentials may
263 not be required. It's conceivable that the use of anonymous mode or
264 the compromise of authentication credentials could lead to the
265 undesired provision of information which could then be used for
266 nefarious purposes. Care must be taken to secure the credentials
267 used by Minger and to police the provision of information when using
268 anonymous mode.
270 5. IANA Considerations
272 Minger requires allocation of a Registered Port by IANA.
274 6. Informative References
276 [RFC1288] Zimmerman, D., "The Finger User Information Protocol",
277 RFC 1288, December 1991.
279 [RFC2821] Klensin, J., Editor, "Simple Mail Transfer Protocol", RFC
280 2821, March 2001.
282 [RFC4234] Crocker, D., Ed. And P. Overell, "Augmented BNF for Syntax
283 Specifications: ABNF", RFC 4234, October 2005.
285 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
286 Requirement Levels", BCP 14, RFC 2119, March 1997.
288 Appendix A. Acknowledgements
290 We wish to thank the members of the MDaemon Beta Community
291 (subscribe-md-beta@altn.com) for their ideas and help.
293 Authors' Addresses
295 Arvel Hathcock
296 Alt-N Technologies
297 http://www.altn.com
299 Email: arvel.hathcock@altn.com
301 Jonathan Merkel
302 Alt-N Technologies
303 http://www.altn.com
305 Email: jon.merkel@altn.com
307 Full Copyright Statement
309 Copyright (C) The IETF Trust (2007).
311 This document is subject to the rights, licenses and restrictions
312 contained in BCP 78, and except as set forth therein, the authors
313 retain all their rights.
315 This document and the information contained herein are provided on an
316 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
317 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
318 THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
319 OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
320 THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
321 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
323 Intellectual Property
325 The IETF takes no position regarding the validity or scope of any
326 Intellectual Property Rights or other rights that might be claimed to
327 pertain to the implementation or use of the technology described in
328 this document or the extent to which any license under such rights
329 might or might not be available; nor does it represent that it has
330 made any independent effort to identify any such rights. Information
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339 http://www.ietf.org/ipr.
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347 Acknowledgment
349 Funding for the RFC Editor function is provided by the IETF
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