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Owl River Company
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Your IP is: 38.107.191.114
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RFC 2821 misconfigurations - missing postmaster and domain acceptance outline
http://www.owlriver.com/tips/smtp-rfc/
- Customer: My cousin says that his email to me is not going through.
- Sysadmin: I'll look into it ...
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
http://www.owlriver.com/tips/smtp-rfc/index.php