I often get undelivered messages sent back to email inbox indicating that unable to deliver message to: Delivery failed for the following reason:
In mail queue too long, giving up.
cause of failure
Server mail[212.88.102.138] failed with: 450 4.1.1 .
Recipient address rejected: undeliverable address: unknown user:
This has been a permanent failure. No further delivery attempts will be made.
what should be done
