If you're already using qmail-smtpd and friends, set up recordio to record all input and output to your mail server. Then you should be able to identify problem sessions, and see what went on.

Alternatively, use a packet sniffer like tcpdump to monitor all traffic with the hosts that are having problems, then review the logs after a problem happens.

A few random thoughts...One problem that seems to particularly plague Windows mail clients is not sending a proper CR/LF pair at the end of each SMTP line. Another possibility is that you're not flushing your socket's output buffer and don't have AutoFlush turned on for it. I had a problem with an SMTP wrapper for qmail-smtpd that turned out to be an improper PIPELINING implementation on my end. All of those are easy to test, and make sure that your system handles them properly.

If none of that helps, well, post some code. :)

In reply to Re: Socket weirdness by sgifford
in thread Socket weirdness by dgaramond2

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