Looking at the SMTP logs on Exchange 2003, many of the entries have a '0' as the response code. And yet the email was delivered successfully. Any idea why? Could these be servers that don't support EHLO? thanks

could you post a sample of your log

In general, it shows that server received connection from PC xx, and there was no SMTP traffic during that period of time, you can try to confirm if there was any abnormality during that period. Or using Message Tracking Center to see if there was any traffic between server and PC xxs OL user

Hi, Akg414s, does it settle your question?

Hi, Akg414s, I suppose it has answered your problem, and I'd like to change the status to "Marked as answer", please feel free to post here if you have any other update