idnits 2.17.1 draft-ietf-msgtrk-smtpext-04.txt: ** The Abstract section seems to be numbered Checking boilerplate required by RFC 5378 and the IETF Trust (see https://trustee.ietf.org/license-info): ---------------------------------------------------------------------------- ** Looks like you're using RFC 2026 boilerplate. This must be updated to follow RFC 3978/3979, as updated by RFC 4748. Checking nits according to https://www.ietf.org/id-info/1id-guidelines.txt: ---------------------------------------------------------------------------- ** Missing expiration date. The document expiration date should appear on the first and last page. ** The document seems to lack a 1id_guidelines paragraph about Internet-Drafts being working documents. ** The document seems to lack a 1id_guidelines paragraph about the list of current Internet-Drafts -- however, there's a paragraph with a matching beginning. Boilerplate error? ** The document seems to lack a 1id_guidelines paragraph about the list of Shadow Directories -- however, there's a paragraph with a matching beginning. Boilerplate error? == No 'Intended status' indicated for this document; assuming Proposed Standard == The page length should not exceed 58 lines per page, but there was 6 longer pages, the longest (page 2) being 62 lines Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- ** The document seems to lack an Introduction section. == The 'Updates: ' line in the draft header should list only the _numbers_ of the RFCs which will be updated by this document (if approved); it should not include the word 'RFC' in the list. -- The draft header indicates that this document updates RFC1891, but the abstract doesn't seem to mention this, which it should. Miscellaneous warnings: ---------------------------------------------------------------------------- (Using the creation date from RFC1891, updated by this document, for RFC5378 checks: 1996-01-01) -- The document seems to lack a disclaimer for pre-RFC5378 work, but may have content which was first submitted before 10 November 2008. If you have contacted all the original authors and they are all willing to grant the BCP78 rights to the IETF Trust, then this is fine, and you can ignore this comment. If not, you may need to add the pre-RFC5378 disclaimer. (See the Legal Provisions document at https://trustee.ietf.org/license-info for more information.) -- The document date (October 21, 2002) is 7857 days in the past. Is this intentional? Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Outdated reference: A later version (-07) exists of draft-ietf-msgtrk-model-03 ** Downref: Normative reference to an Informational draft: draft-ietf-msgtrk-model (ref. 'DRAFT-MTRK-MODEL') == Outdated reference: A later version (-12) exists of draft-ietf-msgtrk-mtqp-01 ** Obsolete normative reference: RFC 2234 (ref. 'RFC-ABNF') (Obsoleted by RFC 4234) ** Obsolete normative reference: RFC 1869 (ref. 'RFC-ESMTP') (Obsoleted by RFC 2821) -- Possible downref: Non-RFC (?) normative reference: ref. 'NIST-SHA1' ** Obsolete normative reference: RFC 2821 (ref. 'RFC-SMTP') (Obsoleted by RFC 5321) -- Obsolete informational reference (is this intentional?): RFC 1891 (ref. 'RFC-DSN-SMTP') (Obsoleted by RFC 3461) -- Obsolete informational reference (is this intentional?): RFC 2298 (ref. 'RFC-MDN') (Obsoleted by RFC 3798) -- Obsolete informational reference (is this intentional?): RFC 1750 (ref. 'RFC-RANDOM') (Obsoleted by RFC 4086) Summary: 11 errors (**), 0 flaws (~~), 5 warnings (==), 7 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Internet Draft E. Allman 3 draft-ietf-msgtrk-smtpext-04.txt Sendmail, Inc. 4 Valid for six months T. Hansen 5 Updates: RFC 1891 AT&T Laboratories 6 October 21, 2002 8 SMTP Service Extension 9 for Message Tracking 11 13 Status of This Memo 15 This document is an Internet-Draft and is in full conformance 16 with all provisions of Section 10 of RFC2026. Internet-Drafts are 17 working documents of the Internet Engineering Task Force (IETF), its 18 areas, and its working groups. Note that other groups may also 19 distribute working documents as 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 documents 23 at any time. It is inappropriate to use Internet-Drafts as reference 24 material or to cite them other than as "work in progress." 26 The IETF takes no position regarding the validity or scope of any 27 intellectual property or other rights that might be claimed to 28 pertain to the implementation or use of the technology described in 29 this document or the extent to which any license under such rights 30 might or might not be available; neither does it represent that it has 31 made any effort to identify any such rights. Information on the 32 IETF's procedures with respect to rights in standards-track and 33 standards-related documentation can be found in BCP-11. Copies of 34 claims of rights made available for publication and any assurances of 35 licenses to be made available, or the result of an attempt made to 36 obtain a general license or permission for the use of such proprietary 37 rights by implementors or users of this specification can be obtained 38 from the IETF Secretariat. 40 The IETF invites any interested party to bring to its attention 41 any copyrights, patents or patent applications, or other proprietary 42 rights which may cover technology that may be required to practice 43 this standard. Please address the information to the IETF Executive 44 Director. 46 The list of current Internet-Drafts can be accessed at: 48 http://www.ietf.org/ietf/1id-abstracts.txt 50 The list of Internet-Draft Shadow Directories can be accessed at: 52 http://www.ietf.org/shadow.html 53 This document is a submission by the MSGTRK Working Group of the 54 Internet Engineering Task Force (IETF). Comments should be submitted 55 to the ietf-msgtrk@imc.org mailing list. An archive of the mailing 56 list may be found at 58 http://www.imc.org/ietf-msgtrk/index.html 60 Distribution of this memo is unlimited. 62 1. Abstract 64 This memo defines an extension to the SMTP service whereby a 65 client may mark a message for future tracking. 67 2. Other Documents and Conformance 69 The model used for Message Tracking is described in [DRAFT- 70 MTRK-MODEL]. 72 Doing a Message Tracking query is intended as a "last resort" 73 mechanism. Normally, Delivery Status Notifications (DSNs) [RFC- 74 DSN-SMTP] and Message Disposition Notifications (MDNs) [RFC-MDN] 75 would provide the primary delivery status. Only if the message is 76 not received, or there is no response from either of these 77 mechanisms should a Message Tracking query be issued. 79 The definition of the base64 token is imported from section 80 6.8 of [RFC-MIME]. 82 Syntax notation in this document conforms to [RFC-ABNF]. 84 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL 85 NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" 86 in this document are to be interpreted as described in RFC 2119 87 [RFC-KEYWORDS]. 89 3. SMTP Extension Overview 91 The Message Tracking SMTP service extension uses the SMTP 92 service extension mechanism described in [RFC-ESMTP]. The 93 following service extension is hereby defined: 95 (1) The name of the SMTP service extension is "Message 96 Tracking". 98 (2) The EHLO keyword value associated with this extension is 99 "MTRK". 101 (3) No parameters are allowed with this EHLO keyword value. 102 Future documents may extend this specification by specifying 103 parameters to this keyword value. 105 (4) One optional parameter using the keyword "MTRK" is added to 106 the MAIL command. In addition, the ENVID parameter of the 107 MAIL command (as defined in RFC 1891 sections 5.4) MUST be 108 supported, with extensions as described below. The ORCPT 109 parameter of the RCPT command (as defined in RFC 1891 110 section 5.2) MUST also be supported. All semantics 111 associated with ENVID and ORCPT described in RFC 1891 MUST 112 be supported as part of this extension. 114 (5) The maximum length of a MAIL command line is increased by 40 115 characters by the possible addition of the MTRK keyword and 116 value. Note that the 507 character extension of RCPT 117 commands for the ORCPT parameter and the 107 character 118 extension of MAIL commands for the ENVID parameter as 119 mandated by RFC 1891 [RFC-DSN-SMTP] must also be included. 121 (6) No SMTP verbs are defined by this extension. 123 4. The Extended MAIL Command 125 The extended MAIL command is issued by an SMTP client when it 126 wishes to inform an SMTP server that message tracking information 127 should be retained for future querying. The extended MAIL command 128 is identical to the MAIL command as defined in [RFC-SMTP], except 129 that MTRK, ORCPT, and ENVID parameters appear after the address. 131 4.1. The MTRK parameter to the ESMTP MAIL command 133 Any sender wishing to request the retention of data for 134 further tracking of message must first tag that message as 135 trackable by creating two values A and B: 137 A = some-large-random-number 138 B = SHA1(A) 140 The large random number A is calculated on a host-dependent 141 basis. See [RFC-RANDOM] for a discussion of choosing good 142 random numbers. This random number MUST be at least 128 bits 143 but MUST NOT be more than 1024 bits. 145 The 128-bit hash B of A is then computed using the SHA-1 146 algorithm as described in [NIST-SHA1]. 148 The sender then base64 encodes value B and passes that 149 value as the mtrk-certifier on the MAIL command: 151 mtrk-parameter = "MTRK=" mtrk-certifier [ ":" mtrk-timeout ] 152 mtrk-certifier = base64 ; authenticator 153 mtrk-timeout = 1*9digit ; seconds until timeout 155 A is stored in the originator's tracking database to 156 validate future tracking requests as described in [DRAFT-MTRK- 157 MTQP]. B is stored in tracking databases of compliant receiver 158 MTAs and used to authenticate future tracking requests. 160 The mtrk-timeout field indicates the number of seconds that 161 the client requests that this tracking information be retained 162 on intermediate servers, as measured from the initial receipt of 163 the message at that server. Servers MAY ignore this value if it 164 violates local policy. In particular, servers MAY silently 165 enforce an upper limit to how long they will retain tracking 166 data; this limit MUST be at least one day. 168 If no mtrk-timeout field is specified then the server 169 should use a local default. This default SHOULD be 8-10 days 170 and MUST be at least one day. Notwithstanding this clause, the 171 information MUST NOT be expired while the message remains in the 172 queue for this server: that is, an MTQP server MUST NOT deny 173 knowledge of a message while that same message sits in the MTA 174 queue. 176 If the message is relayed to another compliant SMTP server, 177 the MTA acting as the client SHOULD pass an mtrk-timeout field 178 equal to the remaining life of that message tracking 179 information. Specifically, the tracking timeout is decremented 180 by the number of seconds the message has lingered at this MTA 181 and then passed to the next MTA. If the decremented tracking 182 timeout is less than or equal to zero, the entire MTRK parameter 183 MUST NOT be passed to the next MTA; essentially, the entire 184 tracking path is considered to be lost at that point. 186 See [RFC-DELIVERYBY] section 4 for an explanation of why a 187 timeout is used instead of an absolute time. 189 4.2. Use of ENVID 191 To function properly, Message Tracking requires that each 192 message have a unique identifier that is never reused by any 193 other message. For that purpose, if the MTRK parameter is 194 given, an ENVID parameter MUST be included, and the syntax of 195 ENVID from RFC 1891 section 5.4 is extended as follows: 197 envid-parameter = "ENVID=" unique-envid 198 unique-envid = local-envid "@" fqhn 199 local-envid = xtext 200 fqhn = xtext 202 The unique-envid MUST be chosen in such a way that the same 203 ENVID will never be used by any other message sent from this 204 system or any other system. In most cases, this means setting 205 fqhn to be the fully qualified host name of the system 206 generating this ENVID, and local-envid to an identifier that is 207 never re-used by that host. 209 In some cases, the total length of (local-envid + fqhn + 1) 210 (for the `@' sign) may exceed the total acceptable length of 211 ENVID (100). In this case, the fqhn SHOULD be replaced by the 212 SHA1(fqhn) encoded into BASE64. After encoding, the 160 bit 213 SHA-1 will be a 27 octet string, which limits local-envid to 72 214 octets. Implementors are encouraged to use an algorithm for the 215 local-envid that is reasonably unique. For example, sequential 216 integers have a high probability of intersecting with sequential 217 integers generated by a different host, but a SHA-1 of the 218 current time of day concatenated with the host's IP address and 219 a random number are unlikely to intersect with the same 220 algorithm generated by a different host. 222 Any resubmissions of this message into the message 223 transmission system MUST assign a new ENVID. In this context, 224 "resubmission" includes forwarding or resending a message from a 225 user agent, but does not include MTA-level aliasing or 226 forwarding where the message does not leave and re-enter the 227 message transmission system. 229 4.3. Forwarding Tracking Certifiers 231 MTAs SHOULD forward unexpired tracking certifiers to 232 compliant mailers as the mail is transferred during regular hop- 233 to-hop transfers. If the "downstream" MTA is not MTRK- 234 compliant, then the MTRK= parameter MUST be deleted. If the 235 downstream MTA is DSN-compliant, then the ENVID and ORCPT 236 parameters MUST NOT be deleted. 238 If aliasing, forwarding, or other redirection of a 239 recipient occurs, and the result of the redirection is exactly 240 one recipient, then the MTA SHOULD treat this as an ordinary 241 hop-to-hop transfer and forward the MTRK=, ENVID=, and ORCPT= 242 values; these values MUST NOT be modified except for 243 decrementing the mtrk-timeout field of the MTRK= value, which 244 MUST be modified as described in section 4.1 above. 246 MTAs MUST NOT copy MTRK certifiers when a recipient is 247 aliased, forwarded, or otherwise redirected and the redirection 248 results in more than one recipient. However, an MTA MAY 249 designate one of the multiple recipients as the "primary" 250 recipient to which tracking requests shall be forwarded; other 251 addresses MUST NOT receive tracking certifiers. MTAs MUST NOT 252 forward MTRK certifiers when doing mailing list expansion. 254 5. Security Considerations 256 5.1. Denial of service 258 An attacker could attempt to flood the database of a server 259 by submitting large numbers of small, tracked messages. In this 260 case, a site may elect to lower its maximum retention period 261 retroactively. 263 5.2. Confidentiality 265 The mtrk-authenticator value (``A'') must be hard to 266 predict and not reused. 268 The originating client must take reasonable precautions to 269 protect the secret. For example, if the secret is stored in a 270 message store (e.g., a "Sent" folder), the client must make sure 271 the secret isn't accessible by attackers, particularly on a 272 shared store. 274 Many site administrators believe that concealing names and 275 topologies of internal systems and networks is an important 276 security feature. MTAs need to balance such desires with the 277 need to provide adequate tracking information. 279 In some cases site administrators may want to treat 280 delivery to an alias as final delivery in order to separate 281 roles from individuals. For example, sites implementing 282 ``postmaster'' or ``webmaster'' as aliases may not wish to 283 expose the identity of those individuals by permitting tracking 284 through those aliases. In other cases, providing the tracking 285 information for an alias is important, such as when the alias 286 points to the user's preferred public address. 288 Therefore, implementors are encouraged to provide 289 mechanisms by which site administrators can choose between these 290 alternatives. 292 6. IANA Considerations 294 IANA is to register the SMTP extension defined in section 3. 296 7. Acknowledgements 298 Several individuals have commented on and enhanced this draft, 299 including Philip Hazel, Alexey Melnikov, Lyndon Nerenberg, Chris 300 Newman, and Gregory Neil Shapiro. 302 8. Normative References 304 [DRAFT-MTRK-MODEL] 305 T. Hansen, ``Message Tracking Model and Requirements.'' 306 draft-ietf-msgtrk-model-03.txt. November 2000. 308 [DRAFT-MTRK-MTQP] 309 T. Hansen, ``Message Tracking Query Protocol.'' draft-ietf- 310 msgtrk-mtqp-01.txt. November 2000. 312 [RFC-ABNF] 313 Crocker, D., Editor, and P. Overell, ``Augmented BNF for 314 Syntax Specifications: ABNF'', RFC 2234, November 1997. 316 [RFC-ESMTP] 317 Rose, M., Stefferud, E., Crocker, D., Klensin, J. and N. 318 Freed, ``SMTP Service Extensions.'' STD 10, RFC 1869. 319 November 1995. 321 [RFC-KEYWORDS] 322 S. Bradner, ``Key words for use in RFCs to Indicate 323 Requirement Levels.'' RFC 2119. March 1997. 325 [RFC-MIME] 326 N. Freed and N. Borenstein, ``Multipurpose Internet Mail 327 Extensions (MIME) Part One: Format of Internet Message 328 Bodies.'' RFC 2045. November 1996. 330 [NIST-SHA1] 331 NIST FIPS PUB 180-1, ``Secure Hash Standard.'' National 332 Institute of Standards and Technology, U.S. Department of 333 Commerce. May 1994. DRAFT. 335 [RFC-SMTP] 336 J. Klensin, editor, ``Simple Mail Transfer Protocol.'' RFC 337 2821. April 2001. 339 9. Informational References 341 [RFC-DELIVERYBY] 342 D. Newman, ``Deliver By SMTP Service Extension.'' RFC 2852. 343 June 2000. 345 [RFC-DSN-SMTP] 346 K. Moore, ``SMTP Service Extension for Delivery Status 347 Notifications.'' RFC 1891. January 1996. 349 [RFC-MDN] 350 R. Fajman, ``An Extensible Message Format for Message 351 Disposition Notifications.'' RFC 2298. March 1998. 353 [RFC-RANDOM] 354 D. Eastlake, S. Crocker, and J. Schiller, ``Randomness 355 Recommendations for Security.'' RFC 1750. December 1994. 357 10. Authors' Addresses 359 Eric Allman 360 Sendmail, Inc. 361 6425 Christie Ave, 4th Floor 362 Emeryville, CA 94608 363 U.S.A. 365 E-Mail: eric@Sendmail.COM 366 Phone: +1 510 594 5501 367 Fax: +1 510 594 5429 369 Tony Hansen 370 AT&T Laboratories 371 Middletown, NJ 07748 372 U.S.A. 374 Phone: +1 732 420 8934 375 E-Mail: tony@att.com