Recently I’ve had a problem like this. I didn’t make any changes, but my account refused to send mail at all. When my logs were read, here is what I got:
2008-09-22 06:50:37 H=MY IP (SERVER) [MY IP] incomplete transaction (connection lost) from <email@example.com>
2008-09-22 06:50:37 unexpected disconnection while reading SMTP command from MY IP (SERVER) [MY IP]
I thounght that’s related to my IP (as my IP is a dynamic one). But everything was ok with other servers and I has to investigate the issue. I’ve tried many solutions, but found no one on the Internet. As usually, I had to figure it out by myself.
The solution was quite simple and was not related to the server. The only thing I had to do was to change the timeout value in my E-mail client (that’s The Bat!). While the default timeout value is 60 seconds, setting it to 120 solves the issue.
This solution should help you on busy servers, that are processing big amounts of data and your e-mails will be always sent in time!