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RE: Still no change ~Karl Eknuplopoopsi 3.Jun.03 12:06 PM a Web browser Domino Server 6.0.1Windows 2000
Interesting.
We did 3 things to reduce the number of occurrences "0 message[s] received".
1. Disabled the fixup protocol on our Cisco Pics firewall. Some hosts are apparently very confused to encounter a 500 response to an EHLO (translated by fixup to XXXX) and so they disconnect immediately before trying again with HELO. Removing fixup protocol had a dramatic effect, reducing the number of instances of "0 message[s]" by c. 80%, but there was still a problem.
2. Disabled ESMTP command pipelining on the Domino host. This fixed most of the remaining issues. Actually, it is a good idea to turn off pipelining anyway as there is a lot of spamware out there which will attempt to pipeline an entire spam and disconnect before any 5.x.x status codes are sent back.
But there were still a few occasions when we would see "0 message[s] received" for no obvious reason. These tended to be infrequent, but would occur in large groups, usually with the same Internet mail host connecting and disconnecting and this often happened several times in the space of a few minutes or less. These servers almost always appeared to be MS Exchange. So your post about MTU sizes got me thinking.
If your ND6 host is on NT/W2K and the remote MS Exchange server is also on NT/W2K (what else), and they both have no MTU size set, then MTU is dynamic, I think negotiated at the time the remote host connects. If these two W2K machines manage between them to negotiate a large MTU size then packet fragmentation is almost inevitable. So...
3. We set the MTU size on our ND6 host to 576.
Since then, the _only_ occurrences of "0 message[s] received" in the log (early days yet, I know) have been when the mail has been rejected by us due to blacklisting or some local policy violation. There has so far been not a single manifestation of "0 message[s] received" that could not be explained in this way.
Of course the downside is that having small MTU sizes on fast Internet connections is rather inefficient. But this is a mail host only, so not really an issue so far as any user is concerned.
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. . . . . . RE: Still no change (~Karl Eknuplopo... 3.Jun.03) 
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