I'm a noob, so forgive any errors in terminology.
I've noticed a pattern. It seems like our A records are all on the same subnet of 64.129.12.xx. Please note: we are not in the same company -- we just send emails to each other. The only coincidence is our IP addresses. This problem only happens with clients on the same IP address pattern.
I can send email to them. They can't send to me. My mail server log says: Winsock Error 10054 Connection was reset by the other side!
My domain name is rnsha.com. Does nslookup provide a clue?
Do you need more info?