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RFC 2821 misconfigurations - missing postmaster and domain acceptance outline

http://www.owlriver.com/tips/smtp-rfc/


We have spoken before about RFC 2821, which governs email exchanges between a sender and receiver Mail Transfer Agent (MTA). We know we can always test toward the mandatory 'postmaster' account -- (required under RFC 2821, section 4.5.1 Minimum Implementation:

... Any system that includes an SMTP server supporting mail relaying or delivery MUST support the reserved mailbox "postmaster" as a case- insensitive local name. ...
for it will always support delivery of email to that special account, if properly configured. (We have sanitized the domain name and the IP in our example).

[herrold@oldnews herrold]$ dig columbusxyz.org mx ; <<>> DiG 9.2.1 <<>> columbusxyz.org mx ;; global options: printcmd ;; Got answer: ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 8178 ;; flags: qr aa rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 4, ADDITIONAL: 4 ;; QUESTION SECTION: ;columbusxyz.org. IN MX ;; ANSWER SECTION: columbusxyz.org. 86400 IN MX 10 mail.columbusxyz.org. <snip> ;; ADDITIONAL SECTION: mail.columbusxyz.org. 86400 IN A 66.93.212.999 <snip> [herrold@oldnews herrold]$
Reading this, we asked the Domain Name System for the identity of the MX -- Main Exchangers -- for the recipient domain. The lowest numbered (closest to final delivery) server is mail.columbusxyz.org.. Looking below, we see that there is a proper association of a A record with mail.columbusxyz.org., pointing to ip: mail.columbusxyz.org..
[herrold@oldnews herrold]$ telnet 66.93.212.999 25 Trying 66.93.212.999... Connected to 66.93.212.999. Escape character is '^]'. 220 lyxyz_ntserver.columbusxyz.org ESMTP Server (Microsoft Exchange Internet Mail Service 5.5.2653.13) ready EHLO asdf 250-lyxyz_ntserver.columbusxyz.org Hello [servera.qn.net] 250-XEXCH50 250-HELP 250-ETRN 250-DSN 250-SIZE 0 250-AUTH LOGIN 250 AUTH=LOGIN MAIL FROM: acme@columbusxyz.org 250 OK - mail from RCPT TO: postmaster@lyxyz_ntserver.columbusxyz.org 550 Relaying is prohibited RCPT TO: postmaster@columbusxyz.org 550 Relaying is prohibited quit 221 closing connection Connection closed by foreign host. [herrold@oldnews herrold]$
Well, that's all we need to solve. They are misconfigured, at a minimum not accepting postmaster email, although seemingly offering to receive email generally. We might suspect that their acceptance domain settings are 'horked up' as well, but that is for another day.

And so we are satisfied that we are conformant to the protocol, and that the problem lies elsewhere beyond our demarc.

Disclaimer: Electronic mail is a 'best efforts' content delivery mechanism. It is not a mechanism with guarantee of delivery; guarantee of 'in order' delivery; nor guarantee of timely delivery. Many people have come to think of email as such, but this is not part of the design specification. If a customer thinks they need any of those attributes, contact us for a system design to meet stated needs.



We make this available for non-commercial and individual use. Please respect our copyright, and consider contacting us for all your Open Source and *nix design, architect / systems analysis, and administration needs.


Copyright (C) 2002 R P Herrold
      herrold@owlriver.com  NIC: RPH5 (US)
   My words are not deathless prose,
      but they are mine.

       Owl River Company
   "The World is Open to Linux (tm)"
   ... Open Source LINUX solutions ...
      info@owlriver.com
         Columbus, OH

- initial 020923 RPH
http://www.owlriver.com/tips/smtp-rfc/

See also in the series:
    trace-sendmail
    tcpflow-tutorial

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Last modified: Thu, 26 Sep 2002 00:42:29 -0400
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