I had a huge backlog to cox.net the other day on one of my servers. Their postmaster gave me the following issues they observed with us, which caused them to temporarily block the server:
1. Your mailserver is attempting to communicate too soon within the SMTP transaction. Ensure that your sending server is RFC 5321-compliant, and is following the proper SMTP protocol standards. 2. Your mailserver is attempting to send more than 100 messages in one session. We are running postfix 2.8.2, so I *really* can't figure out why they'd say item 1 above. They do not advertise pipelining in their EHLO response, and postfix will honor that. They do have a delay between connect and their initial greeting. If you say anything in that time, they drop your connection immediately. As for item 2, the only limit postfix allows me to set is the time that the connection will be reused. The default 300s seems too large for them. How can I approximate the 100 delivery limit using time? I set it to 30s for now and will see if we block with them again.
