View the Mail Queue

sudo mailq

Need details of a message in the queue?
Every message has a Queue ID. Copy the ID after running the mailq command.

sudo find /var/spool/postfix/deferred/ -name ECCB516EB4017 -exec cat {} \;

Delete a message

sudo postsuper -d ECCB516EB4017

Delete all messages in the mail queue

sudo postsuper -d ALL