Delete emails from Postfix queue

On Postfix, to delete emails send by some domain (for example domain.tld), you can use:

mailq | awk '$7 ~ /@domain.tld$/ { print $1 }' | tr -d '*!' | postsuper -d -

To delete from a specific sender:

mailq | awk '$7 ~/^username@domain.tld$/ { print $1 }' | tr -d '*!' | postsuper -d -

Nb: To count all messages in queue use:

mailq | grep -c '^[0-9A-Z]'
# or
mailq | grep -c '^\w'

Useful when your wordpress installation starts sending spam emails.