SMTP no-such-user issues
steve at ibctech.ca
Mon Jun 16 22:47:53 CDT 2008
We are experiencing an issue in regards to SMTP MTA relay responses
regarding 'no such user', and it *apparently* appears to be only
occurring when a particular site attempts to deliver email to us. Any
advice on how to further troubleshoot my issue would be greatly appreciated.
I want to keep this as brief as possible...please bear with me. We have
a cluster of Barracuda Spam Firewalls operating as an SMTP server/client
to a cluster of Qmail MTA/MDA's (with CHKUSR in place).
In short, a user from Sympatico (which now delivers via Hotmail) sends
an email to a list of addresses at our domain in which only a single one
of those addresses is bad, a response is sent back to the Sympatico
client advising that ALL the destination addresses were bad, which is
not the case. It doesn't matter whether the recipients were listed in
the RCPT field, or within the DATA field as Cc: or Bcc:. This is a
nightmare on the helpdesk.
When I attempt to simulate the issue from ANY other mail system that
I've tested (my own personal, GMail etc, etc), the legitimate addresses
receive the message, and the relay agent in question in the test
scenario sends back a 551 for ONLY the invalid recip, as opposed to
including even the valid recips.
Although it has not been yet completely verified via logs that the
client SMTP server sends a QUIT before verifying all of the addresses,
it certainly appears thus far that all of the addresses are put through
the standard verification stages prior to DATA and then gives up, even
if the invalid recipient is the last one passed to our system.
Can anyone else provide advise on how to further troubleshoot this, or
for those who live in my part of North America (Toronto), test it for
themselves who have MTA bounce-no-recip in place, that have access to
the Hotmail mail system (I've confirmed the exact same problem exists
(the 551 is very near identical) from a web-based Hotmail address as
well as Sympatico).
Examples of logs and bounces can be provided if necessary.
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