We have a 2013 Exchange CU2 server with a relay connector configured. Randomly, we get a 421 4.4.1 connection timed out error. There is a scheduled task running on another server sending e-mails out through the relay connector usually between 1:00am and 3:00am each day. Most of the e-mails are delivered fine, but every once in a while the e-mails fail with the time out error.
Have changed tarpit; connectiontimeout and other settings on the relay connector but that hasn't helped. The sending server and the Exchange server are running in the same VMware environment so network connectivity shouldn't be an issue. The Exchange maintenance runs during this time, but don't think that is causing the problem. Could TCP auto-tuning be an issue?
The only thing I seen in the event logs on the server is Event 6002 regarding pinging of the mailbox database being reported by many others. These events happen very consistently right after the connection time out errors. No other events indicating an other issues.
Any suggestions?