Messages are being queued with the message "timed out while sending end of data"

Problem

Random messages appear on the Archive tab with a yellow exclamation icon and you are not receiving those messages on your mail server. When you click the yellow icon, you see one of the following error messages:

• timed out while sending end of data -- message may be sent more than once
• timed out while sending message body
• timeout waiting for client input

In addition, some messages may be going through while others may not.

Solution

This can be caused if you have a Cisco PIX or ASA firewall between your mail server and the Internet. There is a known problem with certain Cisco ASA and PIX routers that interferes with SMTP traffic. The solution is to disable the "SMTP fixup" feature in the Cisco router using the following commands:

• configure terminal
• no fixup protocol smtp 25
• write memory

More information:
https://support.symantec.com/us/en/article.tech148896.html