North American Network Operators Group|
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SMTP no-such-user issues
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.