Error: Postfix - do not list domain example.com in BOTH mydestination and virtual_mailbox_domains

In my case, at least, removing mydomain.com from mydestination cleared things up. On my server, mydestination is just localhost, localhost.localdomain

GREAT SOLUTION, works for me.

Inspecting Postfix’s email queue.

1-  Display a list of queued mail

mailq

or

postqueue -p

To save the output to a text file you can run

mailq > myfile.txt

or

postqueue -p > myfile.txt