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'RFC-MSGFMT' on line 279 looks like a reference -- Missing reference section? 'RFC-RELATED' on line 285 looks like a reference Summary: 10 errors (**), 0 flaws (~~), 9 warnings (==), 20 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 1 Internet Draft E. Allman 2 draft-ietf-msgtrk-smtpext-00.txt Sendmail, Inc. 3 Valid for six months T. Hansen 4 Updates: RFC 1891 AT&T Laboratories 5 December 14, 2000 7 SMTP Service Extension 8 for Message Tracking 10 12 Status of This Memo 14 This document is an Internet-Draft and is in full conformance 15 with all provisions of Section 10 of RFC2026. Internet-Drafts are 16 working documents of the Internet Engineering Task Force (IETF), its 17 areas, and its working groups. Note that other groups may also dis- 18 tribute working documents as Internet-Drafts. 20 Internet-Drafts are draft documents valid for a maximum of six 21 months and may be updated, replaced, or obsoleted by other documents 22 at any time. It is inappropriate to use Internet-Drafts as reference 23 material or to cite them other than as "work in progress." 25 The list of current Internet-Drafts can be accessed at: 27 http://www.ietf.org/ietf/1id-abstracts.txt 29 The list of Internet-Draft Shadow Directories can be accessed at: 31 http://www.ietf.org/shadow.html 33 This document is a submission by the MSGTRK Working Group of the 34 Internet Engineering Task Force (IETF). Comments should be submitted 35 to the msgtrk@imc.org mailing list. An archive of the mailing list 36 may be found at 38 http://www.ietf.org/archive/msgtrk 40 Distribution of this memo is unlimited. 42 1. Abstract 44 This memo defines an extension to the SMTP service whereby a 45 client may mark a message for future tracking. 47 2. Other Documents and Conformance 49 The model used for Message Tracking is described in [DRAFT- 50 MTRK-MODEL]. 52 Doing a Message Tracking query is intended as a "last resort" 53 mechanism. Normally, Delivery Status Notifications (DSNs) [RFC- 54 DSN-SMTP] and Message Disposition Notifications (MDNs) [RFC-MDN] 55 would provide the primary delivery status. Only if the message is 56 not received, or there is no response from either of these mecha- 57 nisms should a Message Tracking query be issued. 59 The definition of the base64 token is imported from section 60 6.8 of [RFC-MIME]. 62 Syntax notation in this document conforms to [RFC-ABNF]. 64 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL 65 NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" 66 in this document are to be interpreted as described in RFC 2119 67 [RFC-KEYWORDS]. 69 3. SMTP Extension Overview 71 The Message Tracking SMTP service extension uses the SMTP ser- 72 vice extension mechanism described in [RFC-ESMTP]. The following 73 service extension is hereby defined: 75 (1) The name of the SMTP service extension is "Message Track- 76 ing". 78 (2) The EHLO keyword value associated with this extension is 79 "MTRK". 81 (3) No parameters are allowed with this EHLO keyword value. 82 Future documents may extend this specification by specifying 83 options. 85 (4) One optional parameter using the keyword "MTRK" is added to 86 the MAIL FROM command. In addition, the ENVID and ORCPT 87 parameters (as defined in RFC 1891 sections 5.4 and 5.2 88 respectively) MUST be supported, with extensions as 89 described below. 91 (5) The maximum length of a MAIL FROM command line is increased 92 by 40 characters by the possible addition of the MTRK key- 93 word and value. Note that a further extension of 614 char- 94 acters for the ORCPT and ENVID parameters is required by 95 RFC-DSN-EXT]. 97 (6) No SMTP verbs are defined by this extension. 99 4. The Extended MAIL FROM Command 101 The extended MAIL FROM command is issued by an SMTP client 102 when it wishes to inform an SMTP server that message tracking 103 information should be retained for future querying. The extended 104 MAIL FROM command is identical to the MAIL FROM command as defined 105 in [RFC-SMTP], except that MTRK, ORCPT, and ENVID parameters appear 106 after the address. 108 4.1. The MTRK parameter to the ESMTP MAIL command 110 Any sender wishing to track a message must first tag that 111 message as trackable by creating two values A and B: 113 A = some-large-random-number 114 B = SHA1(A) 116 The large random number A is calculated on a host-dependent 117 basis as described in [DRAFT-MTRK-MODEL]. See also [RFC-RANDOM] 118 for a discussion of choosing good random numbers. This random 119 number MUST be at least 128 bits but MUST NOT be more than 1024 120 bits. 122 The 128-bit hash B of A is then computed using the SHA-1 123 algorithm as described in [NIST-SHA1]. 125 The sender then base64 encodes value B and passes that 126 value as the mtrk-certifier on the MAIL FROM command: 128 mtrk-parameter = "MTRK=" mtrk-certifier [ ":" mtrk-timeout ] 129 mtrk-certifier = base64 ; authenticator 130 mtrk-timeout = 1*9digit; seconds until timeout 132 A is stored in the originator's tracking database to vali- 133 date future tracking requests as described in [DRAFT-MTRK-MTQP]. 134 B is stored in tracking tracking databases of compliant MTAs and 135 used to authenticate future tracking requests. 137 The mtrk-timeout field indicates the number of seconds that 138 the client requests that this tracking information be retained 139 on intermediate servers, as measured from the initial receipt of 140 the message at that server. Servers MAY ignore this value if it 141 violates local policy. In particular, servers MAY silently 142 enforce an upper limit to how long they will retain tracking 143 data; this limit MUST be at least one day. 145 If no mtrk-timeout field is specified then the server 146 should use a local default. This default SHOULD be 8-10 days 147 and MUST be at least one day. Notwithstanding this clause, the 148 information MUST NOT be expired while the message remains in the 149 queue for this server: that is, an MTQP server MUST NOT deny 150 knowledge of a message while that same message sits in the MTA 151 queue. 153 If the message is relayed to another compliant SMTP server, 154 the MTA acting as the client SHOULD pass an mtrk-timeout field 155 equal to the remaining life of that message tracking informa- 156 tion. Specifically, the tracking timeout is decremented by the 157 number of seconds the message has lingered at this MTA and then 158 passed to the next MTA. If the decremented tracking timeout is 159 less than or equal to zero, the entire MTRK parameter MUST NOT 160 be passed to the next MTA; essentially, the entire tracking path 161 is considered to be lost at that point. 163 See [RFC-DELIVERYBY] section 4 for an explanation of why a 164 timeout is used instead of an absolute time. 166 4.2. Use of ENVID 168 To function properly, Message Tracking requires that each 169 message have a unique identifier that is never reused by any 170 other message. For that purpose, if the MTRK parameter is 171 given, an ENVID parameter MUST be included, and the syntax of 172 ENVID from RFC 1891 section 5.4 is extended as follows: 174 envid-parameter = "ENVID=" unique-envid 175 unique-envid = xtext "@" fqhn 176 fqhn = xtext 178 Any retransmissions of this message MUST assign a new ENVID. In 179 this context, "retransmission" includes forwarding or resending 180 a message. 182 4.3. Forwarding Tracking Certifiers 184 MTAs SHOULD forward unexpired tracking certifiers to com- 185 pliant mailers as the mail is transferred during regular hop-to- 186 hop transfers. If the "downstream" MTA is not MTRK-compliant, 187 then the MTRK= parameter MUST be deleted. If the downstream MTA 188 is DSN-compliant, then the ENVID and ORCPT parameters MUST NOT 189 be deleted. 191 If aliasing, forwarding, or other redirection of messages 192 to a single recipient occurs, then the MTA SHOULD treat this as 193 an ordinary hop-to-hop transfer and forward the MTRK=, ENVID=, 194 and ORCPT= values; these values MUST NOT be modified. 196 MTAs MUST NOT copy MTRK certifiers when relaying a message 197 to multiple recipients. An MTA MAY designate one recipient in a 198 multi-recipient alias as the "primary" recipient to which track- 199 ing requests shall be forwarded; other addresses SHALL NOT 200 receive tracking certifiers. MTAs MUST NOT forward MTRK certi- 201 fiers when doing mailing list expansion. 203 5. Security Issues 204 5.1. Denial of service 206 An attacker could attempt to flood the database of a server 207 by submitting large numbers of small, tracked messages. In this 208 case, a site may elect to lower its maximum retention period 209 retroactively. 211 5.2. Confidentiality 213 The mtrk-authenticator value (``A'') must be hard to pre- 214 dict and not reused. 216 The originating client must take reasonable precautions to 217 protect the secret. For example, if the secret is stored in a 218 message store (e.g., a "Sent" folder), the client must make sure 219 the secret isn't accessible by attackers, particularly on a 220 shared store. 222 MTAs SHOULD take precautions to make certain that message 223 tracking cannot be used to explore internal topologies of net- 224 works. 226 6. References 228 [DRAFT-MTRK-MODEL] 229 T. Hansen, ``Message Tracking Model and Requirements.'' 230 draft-ietf-msgtrk-model-03.txt. November 2000. 232 [DRAFT-MTRK-MTQP] 233 T. Hansen, ``Message Tracking Query Protocol.'' draft-ietf- 234 msgtrk-mtqp-01.txt. November 2000. 236 [RFC-ABNF] 237 Crocker, D., Editor, and P. Overell, ``Augmented BNF for Syn- 238 tax Specifications: ABNF'', RFC 2234, November 1997. 240 [RFC-DELIVERYBY] 241 D. Newman, ``Deliver By SMTP Service Extension.'' RFC 2852. 242 June 2000. 244 [RFC-DSN-REPT] 245 G. Vaudreuil, ``The Multipart/Report Content Type for the 246 Reporting of Mail System Administrative Messages.'' RFC 1892. 247 January 1996. 249 [RFC-DSN-SMTP] 250 K. Moore, ``SMTP Service Extension for Delivery Status Notifi- 251 cations.'' RFC 1891. January 1996. 253 [RFC-DSN-STAT] 254 K. Moore and G. Vaudreuil, ``An Extensible Message Format for 255 Delivery Status Notifications.'' RFC 1894. January 1996. 257 [RFC-EMSSC] 258 G. Vaudreuil, ``Enhanced Mail System Status Codes.'' RFC 259 1893. January 1996. 261 [RFC-ESMTP] 262 Rose, M., Stefferud, E., Crocker, D., Klensin, J. and N. 263 Freed, ``SMTP Service Extensions.'' STD 10, RFC 1869. Novem- 264 ber 1995. 266 [RFC-KEYWORDS] 267 S. Bradner, ``Key words for use in RFCs to Indicate Require- 268 ment Levels.'' RFC 2119. March 1997. 270 [RFC-MDN] 271 R. Fajman, ``An Extensible Message Format for Message Disposi- 272 tion Notifications.'' RFC 2298. March 1998. 274 [RFC-MIME] 275 N. Freed and N. Borenstein, ``Multipurpose Internet Mail 276 Extensions (MIME) Part One: Format of Internet Message Bod- 277 ies.'' RFC 2045. November 1996. 279 [RFC-MSGFMT] 280 D. Crocker, ``Standard for the Format of ARPA Internet Text 281 Messages.'' RFC 822. August 1982. 283 [RFC-RANDOM] 285 [RFC-RELATED] 286 E. Levinson, ``The MIME Multipart/Related Content-type.'' RFC 287 2387. August 1998. 289 [NIST-SHA1] 290 NIST FIPS PUB 180-1, ``Secure Hash Standard.'' National 291 Institute of Standards and Technology, U.S. Department of Com- 292 merce. May 1994. DRAFT. 294 [RFC-SMTP] 295 J. Postel, ``Simple Mail Transport Protocol.'' RFC 821. 296 August 1982. 298 7. Authors' Addresses 300 Eric Allman 301 Sendmail, Inc. 302 6603 Shellmound 303 Emeryville, CA 94608 304 U.S.A. 306 E-Mail: eric@Sendmail.COM 307 Phone: +1 510 594 5501 308 Fax: +1 510 594 5411 309 Tony Hansen 310 AT&T Laboratories 311 Lincroft, NJ 07738 312 U.S.A. 314 Phone: +1 732 576 3207 315 E-Mail: tony@att.com