idnits 2.17.1 draft-hathcock-minger-03.txt: Checking boilerplate required by RFC 5378 and the IETF Trust (see https://trustee.ietf.org/license-info): ---------------------------------------------------------------------------- ** It looks like you're using RFC 3978 boilerplate. You should update this to the boilerplate described in the IETF Trust License Policy document (see https://trustee.ietf.org/license-info), which is required now. -- Found old boilerplate from RFC 3978, Section 5.1 on line 14. -- Found old boilerplate from RFC 3978, Section 5.5, updated by RFC 4748 on line 314. -- Found old boilerplate from RFC 3979, Section 5, paragraph 1 on line 325. -- Found old boilerplate from RFC 3979, Section 5, paragraph 2 on line 332. -- Found old boilerplate from RFC 3979, Section 5, paragraph 3 on line 338. Checking nits according to https://www.ietf.org/id-info/1id-guidelines.txt: ---------------------------------------------------------------------------- == The page length should not exceed 58 lines per page, but there was 1 longer page, the longest (page 2) being 108 lines == It seems as if not all pages are separated by form feeds - found 0 form feeds but 9 pages Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- ** There are 3 instances of too long lines in the document, the longest one being 1 character in excess of 72. Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust Copyright Line does not match the current year -- 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 (April 1, 2008) is 5868 days in the past. Is this intentional? Checking references for intended status: Informational ---------------------------------------------------------------------------- -- Obsolete informational reference (is this intentional?): RFC 1734 (Obsoleted by RFC 5034) -- Obsolete informational reference (is this intentional?): RFC 2821 (Obsoleted by RFC 5321) -- Obsolete informational reference (is this intentional?): RFC 4234 (Obsoleted by RFC 5234) Summary: 2 errors (**), 0 flaws (~~), 3 warnings (==), 10 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 1 Network Working Group A. Hathcock 2 Internet-Draft J. Merkel 3 Intended Status: Informational Alt-N Technologies 4 Expires: October 1, 2007 April 1, 2008 6 The Minger Email Address Verification Protocol 7 draft-hathcock-minger-03.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 Internet- 19 Drafts. 21 Internet-Drafts are draft documents valid for a maximum of six months 22 and may be updated, replaced, or obsoleted by other documents at any 23 time. It is inappropriate to use Internet-Drafts as reference 24 material or to cite them other than as "work in progress." 26 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 30 http://www.ietf.org/shadow.html. 32 This Internet-Draft will expire on September 6, 2007. 34 Copyright Notice 36 Copyright (C) The IETF Trust (2007). 38 Abstract 40 This document describes the Minger protocol. Minger is a protocol 41 which allows a mail handling entity to query a remote service and 42 ask the question "do you accept mail for this email address?" It 43 includes security in the form of a hashed shared secret but can also 44 be used anonymously if desired. 46 Requirements Language 48 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 49 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 50 document are to be interpreted as described in [RFC2119]. 52 Table of Contents 54 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 55 1.1. The problem . . . . . . . . . . . . . . . . . . . . . . 3 56 1.2. Existing solutions . . . . . . . . . . . . . . . . . . . 3 57 1.3. The Minger solution . . . . . . . . . . . . . . . . . . 4 58 2. The Minger protocol . . . . . . . . . . . . . . . . . . . . 4 59 2.1 The Minger query process . . . . . . . . . . . . . . . . 4 60 2.2 Description of query elements . . . . . . . . . . . . . . 5 61 3. Minger responses . . . . . . . . . . . . . . . . . . . . . . 5 62 3.1 Description of response elements . . . . . . . . . . . . 5 63 3.2 Example responses . . . . . . . . . . . . . . . . . . . . 6 64 4. Anonymous mode . . . . . . . . . . . . . . . . . . . . . . . 6 65 5. Security Considerations . . . . . . . . . . . . . . . . . . 7 66 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . 7 67 7. Informative References . . . . . . . . . . . . . . . . . . . 7 68 Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . 8 69 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8 70 Intellectual Property and Copyright Statements . . . . . . . . . 9 72 1. Introduction 74 1.1 The problem 76 It is common for elements within a typical email handling topology 77 to be unaware of whether individual local-parts are valid for the 78 mail it accepts. For example, so-called "edge" servers which provide 79 security oriented services for downstream mail handling elements 80 often do not have an exhaustive listing of all valid local-parts for 81 a given domain. Thus, they are sometimes forced to accept and process 82 messages which might otherwise be rejected as "user unknown". 83 Similarly, entities offering "backup MX" mail services are rarely 84 privy to a complete local-part listing and are therefore forced to 85 accept messages which might otherwise be rejected. Finally, even 86 within a common administrative framework of several locally maintained 87 and controlled SMTP servers in a load balanced configuration, it is 88 not always possible for all servers to access a common local-part 89 database. 91 1.2 Existing solutions 93 The need to determine whether an email address contains a valid local 94 part has lead to the use of at least two existing mechanisms - Finger 95 [RFC1288] and SMTP "call-back" / "call-forward". 97 Finger [RFC1288] describes a protocol for the exchange of user 98 information. In theory, Finger could be used to determine whether an 99 account exists by careful examination of the results of a Finger 100 query. However, Finger suffers from a lack of security which makes 101 its modern day use problematic when coupled with the user level 102 detail it can provide. Also, Finger requires the use of TCP rather 103 than UDP which seems ill suited to a simple verification scheme. 105 SMTP "call-back" and "call-forward" are terms describing a widespread 106 practice whereby SMTP servers place an incoming SMTP session on hold 107 while they attempt to use an outbound SMTP session to determine 108 whether or not a given email address is valid. The theory behind this 109 is as follows: if an SMTP server responds positively to an SMTP RCPT 110 or MAIL command [RFC2821] with a given email address then this 111 potentially means that the address local part is valid. One problem 112 with such a scheme is the lack of efficiency inherent in the need to 113 tear-up and tear-down an SMTP session over TCP. Also, because these 114 types of SMTP sessions are not purposed to deliver mail, they 115 typically drop connection after the RCPT command is processed. This 116 leads to a large number of SMTP sessions which appear in logs to have 117 simply failed for no reason. This leads to situations in which SMTP 118 transaction logs can no longer distinguish legitimate network errors 119 from "call-back"/"call-forward" traffic. 121 SMTP includes a VRFY command which can be used to determine whether 122 an email address exits. VRFY is not in wide-spread use and suffers 123 from the same inefficiency concerns described in the discussion on 124 SMTP "call-back". Additionally, a particular SMTP agent serving a 125 domain that has several is not necessarily authoritative making a 126 VRFY request to it potentially unreliable. 128 1.3 The Minger solution 130 What's needed is a protocol which is secure, has little overhead, and 131 can be easily invoked to determine whether a given email address is 132 valid or not. Minger achieves these goals using a shared secret for 133 security and UDP to lower overhead. 135 2. The Minger protocol 137 Minger is a UDP protocol that operates on port 4069. 139 Syntax descriptions use the form described in Augmented Backus-Naur 140 Form for Syntax Specifications (ABNF) [RFC4234]. 142 2.1 The Minger query process 144 A Minger client constructs a query string as described below and 145 transmits it over UDP to a Minger server. The format of the query 146 is as follows: 148 ABNF: 150 query-string = mailbox [SP "d=" digest] [SP tag-list] 152 digest = base64 ; digest for security 153 ; base64 defined in [RFC1734] 155 digest-text = shared-secret ":" mailbox ; input text for digest 157 mailbox = Local-part "@" Domain ; as defined in [RFC2821] 159 shared-secret = 1*50(VCHAR) ; password credential 161 tag-list = tag-spec 0*(SP tag-spec) ; tag/value list 163 tag-spec = tag-name "=" tag-value 164 tag-name = 1 * (any ALPHA other than 'd' / DIGIT / "_") 166 tag-value = 1 * (ALPHA / DIGIT / "_") 168 2.2 Description of query elements 170 mailbox 172 This is the email address for which verification of 173 existence is desired. 175 digest 177 This is the base64 encoding of the MD5 [RFC1321] hash of 178 digest-text. Digest-text is constructed, the MD5 hash of that 179 is computed, and that result is base64 encoded. 181 tag-list 183 Tag-list is provided so that future capability might be added 184 in an easy way. 186 3. Minger responses 188 Minger servers return a response string of the following form: 190 ABNF: 192 response-string = mailbox status 194 mailbox = Local-part "@" Domain ; as defined in [RFC2821] 196 status = %x30-35 ; single digit result code 197 ; from 0 - 5 199 3.1 Description of response elements 201 mailbox 203 This is the email address for which verification of 204 existence is desired. 206 status 208 The following status codes are defined: 210 0 - invalid request (for example, malformed query string) 211 1 - access denied (for example, query from unauthorized IP) 212 2 - bad or missing credentials (returned when anonymous 213 mode is disabled and no credentials were provided in the 214 query string or when the credentials themselves are 215 invalid) 216 3 - email address does not exist 217 4 - email address exists but can not receive mail (for example, 218 the account associated with the email address has exceeded 219 local storage constraints or it is otherwise disabled due 220 to local policy) 221 5 - email address exists and is active (able to receive mail) 223 3.2 Example responses 225 Minger response returned when the queried email address does 226 not exist: 228 arvel@example.com 3 230 Minger response returned for invalid credentials: 232 arvel@example.com 2 234 Minger response returned when the queried email address exists: 236 arvel@example.com 5 238 4. Anonymous mode 240 Minger clients MAY attempt anonymous queries; that is, queries which 241 do not contain a shared secret digest within the query string. Minger 242 servers MAY be configured to refuse anonymous queries. If so, they 243 MUST respond with a status of "2". 245 5. Security Considerations 247 Minger is a protocol which is used to determine whether a given 248 email address is valid or not. If a particular email 249 infrastructure does not wish to advertise the email addresses that 250 it services then this protocol should not be employed. 252 If a shared secret is employed to secure Minger from anonymous use 253 that shared secret should be at least 128 bits. 255 6. IANA Considerations 257 IANA has assigned tcp & upd port 4069 for Minger. 259 7. Informative References 261 [RFC1288] Zimmerman, D., "The Finger User Information Protocol", 262 RFC 1288, December 1991. 264 [RFC1734] Myers, J., "POP3 Authentication Command", RFC 1734, 265 December 1994. 267 [RFC2821] Klensin, J., Editor, "Simple Mail Transfer Protocol", RFC 268 2821, March 2001. 270 [RFC4234] Crocker, D., Ed. And P. Overell, "Augmented BNF for Syntax 271 Specifications: ABNF", RFC 4234, October 2005. 273 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 274 Requirement Levels", BCP 14, RFC 2119, March 1997. 276 [RFC1321] Rivest, R., "The MD5 Message Digest Algorithm", RFC 1321, 277 MIT Laboratory for Computer Science and RSA Data Security, 278 Inc., April 1992. 280 Appendix A. Acknowledgements 282 We wish to thank the members of the MDaemon Beta Community 283 (md-beta-subscribe@altn.com) for their ideas and help and Paul 284 Hoffman for his valuable feedback. 286 Authors' Addresses 288 Arvel Hathcock 289 Alt-N Technologies 290 http://www.altn.com 292 Email: arvel.hathcock@altn.com 294 Jonathan Merkel 295 Alt-N Technologies 296 http://www.altn.com 298 Email: jon.merkel@altn.com 300 Full Copyright Statement 302 Copyright (C) The IETF Trust (2007). 304 This document is subject to the rights, licenses and restrictions 305 contained in BCP 78, and except as set forth therein, the authors 306 retain all their rights. 308 This document and the information contained herein are provided on an 309 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS 310 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND 311 THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS 312 OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF 313 THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED 314 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 316 Intellectual Property 318 The IETF takes no position regarding the validity or scope of any 319 Intellectual Property Rights or other rights that might be claimed to 320 pertain to the implementation or use of the technology described in 321 this document or the extent to which any license under such rights 322 might or might not be available; nor does it represent that it has 323 made any independent effort to identify any such rights. Information 324 on the procedures with respect to rights in RFC documents can be 325 found in BCP 78 and BCP 79. 327 Copies of IPR disclosures made to the IETF Secretariat and any 328 assurances of licenses to be made available, or the result of an 329 attempt made to obtain a general license or permission for the use of 330 such proprietary rights by implementers or users of this 331 specification can be obtained from the IETF on-line IPR repository at 332 http://www.ietf.org/ipr. 334 The IETF invites any interested party to bring to its attention any 335 copyrights, patents or patent applications, or other proprietary 336 rights that may cover technology that may be required to implement 337 this standard. Please address the information to the IETF at 338 ietf-ipr@ietf.org. 340 Acknowledgment 342 Funding for the RFC Editor function is provided by the IETF 343 Administrative Support Activity (IASA).