Recently, I have upgraded the firmware of my ASA firewall and started to experience SMTP problems. Both inbound and outbound SMTP connections are affected.
On the Outbound SMTP Queue, it states that "The connection was dropped by the remote host." The SMTP logs show "4.7.0 Timeout waiting for client input"
On my firewall log, it says "Teardown TCP connection 533110 for outside:18.104.22.168/41624 to inside 192.168.1.5/25 duration 0:05:15 bytes 471418 TCP Reset-O"
I simply cannot figure out what is causing the disconnections. Strange thing is some SMTP connections are getting through, I am still getting emails and able to send out. This means that my firewall is not blocking the SMTP.
But the delivery and sending queue is getting jammed up.