Rob A: > We are having issues sending emails with attachments over ~2 MB to some > recipients. In the situations were we have an error, the remote server > responds with "421 4.4.2 service timed out. (in reply to end of DATA > command)".
If the problem is really size dependent (email does not go no matter how often Postfix retries), then look for TCP window scaling issues (some borked firewall is mis-handling the WSCALE option). A tcpdump recording (no packet payload needed) should reveal that. You can find several examples of this in Postfix archives from a few years ago. Postfix has a tcp_windowsize feature that I implemented for this at the time, but I don't recall if it really addresses the problem. http://www.postfix.org/postconf.5.html#tcp_windowsize Wietse
