SMTP no-such-user issues

[Steve Bertrand <steve () ibctech ca>]

Hi everyone,

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.

Thanks,

Steve