To flush or purge the postfix mail queue, just enter this command
postfix -f
But if you need to delete an individual email from the queue, you'll first need to see the queue. Traditionally you use mailq this time we'll use:
postqueue -p
And the output should show all messages in queue:
5642B4D8647* 1683500 Tue Jun 3 08:37:27 [email protected]
[email protected]
9359B4D82B1* 1635730 Tue Jun 3 08:36:53 [email protected]
[email protected]
The first number is the message ID, if you only want to delete one of them, enter:
postsuper -d 5642B4D8647
That will only delete one email for the queue, that specific email you want to delete from it.
If you want to delete all deferred mails, you can use:
postsuper -d deferred