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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 1 Network Working Group Jutta Degener 2 Internet Draft Philip Guenther 3 Expires: February 2006 Sendmail, Inc. 4 August 2005 6 Sieve Email Filtering: Editheader Extension 7 draft-ietf-sieve-editheader-02.txt 9 Status of this memo 11 By submitting this Internet-Draft, each author represents that any 12 applicable patent or other IPR claims of which he or she is aware 13 have been or will be disclosed, and any of which he or she becomes 14 aware will be disclosed, in accordance with Section 6 of BCP 79. 16 Internet-Drafts are working documents of the Internet Engineering 17 Task Force (IETF), its areas, and its working groups. Note that 18 other groups may also distribute working documents as 19 Internet-Drafts. 21 Internet-Drafts are draft documents valid for a maximum of six 22 months and may be updated, replaced, or obsoleted by other 23 documents at any time. It is inappropriate to use Internet- 24 Drafts as reference material or to cite them other than as 25 "work in progress." 27 The list of current Internet-Drafts can be accessed at 28 http://www.ietf.org/1id-abstracts.html 30 The list of Internet-Draft Shadow Directories can be accessed at 31 http://www.ietf.org/shadow.html 33 Copyright Notice 35 Copyright (C) The Internet Society (2005). 37 Abstract 39 This document defines two new actions for the "Sieve" email 40 filtering language that add and delete email header fields. 42 1. Introduction 44 Email header fields are a flexible and easy to understand means 45 of communication between email processors. 46 This extension enables sieve scripts to interact with other 47 components that consume or produce header fields by allowing 48 the script to delete and add header fields. 50 2. Conventions used. 52 Conventions for notations are as in [SIEVE] section 1.1, including 53 use of [KEYWORDS] and the "Syntax:" label for the definition of 54 action and tagged arguments syntax. 56 The term "header field" is used here as in [IMAIL] to mean a 57 logical line of an email message header. 59 The capability string associated with the extension defined in 60 this document is "editheader". 62 3. Action addheader 64 Syntax: "addheader" [":last"] 66 The addheader action adds a header field to the existing message 67 header. The field-name MUST be a valid 7-bit US-ASCII header 68 field name as described by the [IMAIL] "field-name" nonterminal 69 syntax element. The addheader action does not affect Sieve's 70 implicit keep. 72 If the specified field value does not match the RFC 2822 73 "unstructured" nonterminal syntax element or exceeds a length 74 limit set by the implementation, the implementation MUST either 75 flag an error or encode the field using folding white space and 76 the encodings described in [RFC2047] or [RFC2231] to be compliant 77 with RFC 2822. 79 An implementation MAY impose a length limit onto the size of 80 the encoded header field; such a limit MUST NOT be less 81 than 998 characters, not including the terminating CRLF 82 supplied by the implementation. 84 By default, the header field is inserted at the beginning of the 85 existing message header. If the optional flag ":last" is 86 specified, it is appended at the end. 88 Example: 89 /* Don't redirect if we already redirected */ 90 if not header :contains "X-Sieve-Filtered" 91 ["", ""] 92 { 93 addheader "X-Sieve-Filtered" ""; 94 redirect "kim@home.example.com"; 95 } 97 4. Action deleteheader 99 Syntax: "deleteheader" [":index" [":last"]] 100 [COMPARATOR] [MATCH-TYPE] 101 102 [] 104 By default, the deleteheader action deletes all occurrences of 105 the named header field. The deleteheader action does not affect 106 Sieve's implicit keep. 108 The field-name is mandatory and always matched as a 109 case-insensitive US-ASCII string. The value-patterns, 110 if specified, are matched according to the match type and 111 comparator. If none are specified, all values match. 113 The field-name MUST be a valid 7-bit header field name as described 114 by the [IMAIL] "field-name" nonterminal syntax element. 116 If :index is specified, the attempts to match a value 117 are limited to the occurrence of the named header 118 field, beginning at 1, the first named header field. If :last 119 is specified, the count is backwards; 1 denotes the last named 120 header field, 2 the second to last, and so on. The counting 121 happens before the match, if any. For example: 123 deleteheader :index 2 :contains "Received" "via carrier-pigeon" 125 deletes the second "Received:" header field if it contains 126 the string "via carrier-pigeon" (not the second Received: field 127 that contains "via carrier-pigeon"). 129 It is not an error if no header fields match the conditions in 130 the deleteheader action or if the :index argument is greater 131 than the number of named header fields. 133 5. Interaction with Other Sieve Extensions 135 Tests and actions such as "exists", "header", or "vacation" 136 [VACATION] that examine header fields MUST examine the current 137 state of a header as modified by any actions that have taken 138 place so far. 140 As an example, the "header" test in the following fragment will 141 always evaluate to true, regardless of whether the incoming 142 message contained an "X-Hello" header field or not: 144 addheader "X-Hello" "World"; 145 if header :contains "X-Hello" "World" 146 { 147 fileinto "international"; 148 } 150 However, if the presence or value of a header field affects how 151 the implementation parses or decodes other parts of the message, 152 then for the purposes of that parsing or decoding the implementation 153 MAY ignore some or all changes made to those header fields. For 154 example, in an implementation that supports the [BODY] extension, 155 "body" tests may be unaffected by deleting or adding Content-Type 156 or Content-Transfer-Encoding header fields. This does not rescind 157 the requirement that changes to those header fields affect direct 158 tests; only the semantic side effects of changes to the fields 159 may be ignored. 161 Actions that store or send the message MUST do so with the current 162 set of header fields. 164 For the purpose of weeding out duplicates, a message modified 165 by addheader or deleteheader MUST be considered the same as 166 the original message. For example, in an implementation that 167 obeys the constraint in [SIEVE] section 2.10.3 and does not deliver 168 the same message to a folder more than once, the following 169 code fragment 171 keep; 172 addheader "X-Flavor" "vanilla"; 173 keep; 175 MUST only file one message. It is up to the implementation 176 to pick which of the redundant "fileinto" or "keep" actions is 177 executed, and which ones are ignored. 179 The "implicit keep" is thought to be executed at the end of 180 the script, after the headers have been modified. (However, 181 a canceled "implicit keep" remains canceled.) 183 6. IANA Considerations 185 The following template specifies the IANA registration of the Sieve 186 extension specified in this document: 188 To: iana@iana.org 189 Subject: Registration of new Sieve extension 191 Capability name: editheader 192 Capability keyword: editheader 193 Capability arguments: N/A 194 Standards Track/IESG-approved experimental RFC number: this RFC 195 Person and email address to contact for further information: 197 Jutta Degener 198 jutta@pobox.com 200 This information should be added to the list of sieve extensions 201 given on http://www.iana.org/assignments/sieve-extensions. 203 7. Security Considerations 205 Someone with write access to a user's script storage may use this 206 extension to generate headers that a user would otherwise be 207 shielded from (by a gateway MTA that removes them). 209 A sieve filter that removes header fields may unwisely destroy 210 evidence about the path a message has taken. 212 Any change in a message content may interfere with digital 213 signature mechanisms that include the header in the signed 214 material. Since normal message delivery adds "Received:" 215 header fields to the beginning of a message, many such schemas 216 are impervious to headers prefixed to a message, and will 217 work with "addheader" unless :last is used. 219 Any decision mechanism in a user's filter that is based 220 on headers is vulnerable to header spoofing. For example, 221 if the user adds an APPROVED header or tag, a malicious sender 222 may add that tag or header themselves. One way to guard against 223 this is to delete or rename any such headers or stamps prior 224 to processing the message. 226 Modifying the header of a message and then using the "reject" 227 action may let a sender 'probe' the logic of the sieve filter. 229 8. Acknowledgments 231 Thanks to Eric Allman, Cyrus Daboo, Matthew Elvey, Ned Freed, 232 Arnt Gulbrandsen, Simon Josefsson, Will Lee, William Leibzon, 233 Mark E. Mallett, Chris Markle, Randall Schwartz, Nigel Swinson, 234 Kjetil Torgrim Homme, and Rand Wacker for extensive corrections 235 and suggestions. 237 9. Authors' Addresses 239 Jutta Degener 240 5245 College Ave, Suite #127 241 Oakland, CA 94618 243 Email: jutta@pobox.com 245 Philip Guenther 246 Sendmail, Inc. 247 6425 Christie Ave, 4th Floor 248 Emeryville, CA 94608 250 Email: guenther@sendmail.com 252 10. Discussion 254 This section will be removed when this document leaves the 255 Internet-Draft stage. 257 This draft is intended as an extension to the Sieve mail filtering 258 language. Sieve extensions are discussed on the MTA Filters mailing 259 list at . Subscription requests can 260 be sent to (send an email 261 message with the word "subscribe" in the body). 263 More information on the mailing list along with a WWW archive of 264 back messages is available at . 266 10.1 Changes from draft-ietf-sieve-editheader-01.txt 268 Whitespace and line length tweaks noted by ID-nits. 270 Clarified what is being counted by :index. 272 Update the [SIEVE] reference to the I-D of the revision. 274 10.2 Changes from draft-ietf-sieve-editheader-00.txt 276 Updated IPR boilerplate to RFC 3978/3979. 278 Many corrections in response to WGLC comments. Of particular note: 279 - correct a number of spelling and grammar errors 280 - document that neither addheader nor deleteheader affects the 281 implicit keep 282 - add normative references to RFC 2047 and RFC 2231 283 - it is not an error for deleteheader to affect nothing 284 - change "foo.tld" to "foo.example.com" 285 - add an informative reference to [VACATION], citing it as an 286 example of an action that examines header fields 287 - add weasel words about changes to fields that have secondary 288 effects 289 - add security consideration for combination of header changes 290 and "reject" 292 10.3 Changes from draft-degener-sieve-editheader-03.txt 294 Renamed to draft-ietf-sieve-editheader-00.txt; 295 tweaked the title and abstract. 297 Added Philip Guenther as co-author. 299 Updated IPR boilerplate. 301 10.4 Changes from draft-degener-sieve-editheader-02.txt 303 Changed the duplicate restrictions from "messages with different 304 headers MUST be considered different" to their direct opposite, 305 "messages with different headers MUST be considered the same," 306 as requested by workgroup members on the mailing list. 308 Expanded mention of header signature schemes to Security 309 Considerations. 311 Added IANA Considerations section. 313 Appendices 315 Appendix A. Normative References 317 [IMAIL] Resnick, P., "Internet Message Format", RFC 2822, April 318 2001. 320 [KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate 321 Requirement Levels", RFC 2119, March 1997. 323 [RFC2047] Moore, K., "MIME (Multipurpose Internet Mail 324 Extensions) Part Three: Message Header Extensions for 325 Non-ASCII Text", RFC 2047, November 1996. 327 [RFC2231] Freed, N. and K. Moore, "MIME Parameter Value and 328 Encoded Word Extensions: Character Sets, Languages, and 329 Continuations", RFC 2231, November 1997. 331 [SIEVE] Guenther, P. and T. Showalter, "Sieve: A Mail Filtering 332 Language", draft-ietf-sieve-3028bis-04, July 2005. 334 Appendix B. Informative References 336 [VACATION] Showalter, T. and N. Freed, "Sieve Email Filtering: 337 Vacation Extension", draft-ietf-sieve-vacation-02, 338 April 2005 340 Copyright Statement 342 Copyright (C) The Internet Society (2005). 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