The error message "5.4.7 - Delivery expired (message too old) '[Errno 0] Error'" indicates an issue with email delivery. This error typically occurs when the email message takes too long to be delivered and eventually times out. Here are some steps to troubleshoot and resolve this issue.
Check Network Connectivity and Latency,
Verify that DNS resolution is working correctly and that the ESA can resolve the MX (Mail Exchange) records for the specific domain you are trying to send the email to.
Check the message queues on the ESA to see if the message is stuck or delayed. If there are a large number of messages in the queue, it may indicate an overload or performance issue.
Ensure that the recipient's email address is correct and properly formatted. A typo or incorrect email address can cause delivery issues.
If the issue persists, reach out to the administrator of the destination domain to confirm if they are experiencing any issues with their email server or if there are any restrictions in place.
If the issue persists and you are unable to resolve it, consider reaching out to Cisco TAC for further assistance. Provide with the error message and any relevant log information.
