[exim] Sporadic "relaying not permitted" errors

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Author: Christian Balzer
Date:  
To: exim-users
Subject: [exim] Sporadic "relaying not permitted" errors

Hello,

Exim 4.72-6 (Debian Squeeze, custom single config file).
Mailbox servers handling about 500k mails/day, up to 600 mails/min.
Users (including maildir location) are handled with LDAP.

I've seen the above "relaying not permitted" error about two dozen times
since these machines started to get more traffic (mailboxes where slowly
migrated to them), once I've seen 10 rejects in a second. For addresses
that are and were clearly local at the time and in fact worked a few
seconds before and after that incident.

So the first suspect of course was DNS having a bad hair day and I made
sure that all local domains are in /etc/hosts, nsswitch.conf having the
proper "files dns" order. Restarted exim after adding everything
to /etc/hosts and silence until I got 2 more rejects today.

If LDAP were the culprit I'd expect a different (user not found) error so
I'm rather stumped and puzzled at this time.

Is there any scenario anybody can think of how a relaying not permitted
error can occur given the data above?

The only thing I can think of is DNS returning an actually flawed/false MX
record pointing somewhere not local at the time, any kind of timeout
should not be able to cause this error.

Regards,

Christian
-- 
Christian Balzer        Network/Systems Engineer                
chibi@???       Global OnLine Japan/Fusion Communications
http://www.gol.com/