STOP! FREEZE!

Every so often I find myself wondering how to convince Postfix to hold all mail passing through, so I can make a test that won’t embarrassingly bounce off the next hop. I can never remember how I did it the last time.

header_checks = static:HOLD

This is probably the simplest solution for turning Postfix into a dark-gray hole. It will hold absolutely all (valid) messages that arrive via the SMTP server or are created locally.

To let them go again:

mailq | fgrep \! | cut -d\! -f 1 | postsuper -H -

A ! appended to the queue ID indicates that the message is in the “held” queue.

Individual messages are deleted with

postsuper -d (queue_id)

, i.e. the ID without the !.