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Mail server spitting back Email

Posted on 2000-03-06
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Last Modified: 2013-12-16
I am running Slackware with sendmail running as pop3 and smtp server

When people try to send mail to the server

someone@mydomain.com

Mail servers are spitting it back saying that it is looping back to them, and maybe its an MX problem

This server was working fine and I don't know what happened to it??

Any help is greatly appreciated
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Question by:eric007
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Expert Comment

by:RobWMartin
ID: 2589147
Do you administrate the DNS that advertises your mail server?  If so, can you post the relevant parts of your zone file, esp. the MX record and anything mentioning mydomain.com.  Also, can we see the exact error message?

Thx
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Accepted Solution

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jlevie earned 300 total points
ID: 2589521
There could be a DNS problem, but more likely the problem is the sendmail config. The Sendmail FAQ says:

I'm getting these error messages:

        553 MX list for domain.net points back to relay.domain.net
        554 <user@domain.net>... Local configuration error

How can I solve this problem?

You have asked mail to the domain (e.g., domain.net) to be forwarded to a specific host (in this case, relay.domain.net) by using an MX record, but
the relay machine doesn't recognize itself as domain.net. Add domain.net to /etc/sendmail.cw (if you are using FEATURE(use_cw_file)) or add "Cw
domain.net" to your configuration file.

IMPORTANT: When making changes to your configuration file, be sure you kill and restart the sendmail daemon (for ANY change in the
configuration, not just this one):
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Expert Comment

by:jlevie
ID: 2589539
Oh yeah, if it's a DNS problem the usual cause, per the sendmail FAQ (http://www.sendmail.org/faq/), is:

Wildcard MX records have lots of semantic "gotcha"s. For example, they will match a host "unknown.your.domain" -- if you don't explicitly test for
unknown hosts in your domain, you will get "MX list for hostname points back to hostname" or "config error: mail loops back to myself".

See RFCs 1535, 1536, and 1912 (updates RFC 1537) for more detail and other related (or common) problems. See also _DNS and BIND_ by
Albitz and Liu.

They can also cause your system to add your domain to outgoing FQDNs in a desperate attempt to get the mail to where it's supposed to go, but
because *.your.domain is valid due to the wildcard MX, delivery to not.real.domain.your.domain will get dumped on you, and you may even find
yourself in a loop as the domain keeps getting tacked on time after time after time (the "config error: mail loops back to myself" problem).

Wildcard MX records are just a bad idea, plain and simple. They don't work the way you'd expect, and virtually no one gets them right. Avoid them
at all costs.
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