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(See the Legal Provisions document at https://trustee.ietf.org/license-info for more information.) -- The document date (March 6, 2007) is 6258 days in the past. Is this intentional? Checking references for intended status: Informational ---------------------------------------------------------------------------- -- 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: 1 error (**), 0 flaws (~~), 2 warnings (==), 9 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 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) "") 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 331 on the procedures with respect to rights in RFC documents can be 332 found in BCP 78 and BCP 79. 334 Copies of IPR disclosures made to the IETF Secretariat and any 335 assurances of licenses to be made available, or the result of an 336 attempt made to obtain a general license or permission for the use of 337 such proprietary rights by implementers or users of this 338 specification can be obtained from the IETF on-line IPR repository at 339 http://www.ietf.org/ipr. 341 The IETF invites any interested party to bring to its attention any 342 copyrights, patents or patent applications, or other proprietary 343 rights that may cover technology that may be required to implement 344 this standard. Please address the information to the IETF at 345 ietf-ipr@ietf.org. 347 Acknowledgment 349 Funding for the RFC Editor function is provided by the IETF 350 Administrative Support Activity (IASA).