Smtp – queue

List messages:

mailq
or
postqueue -p

View message content:

postcat -vq <msgId>

Reprocess messages:

postqueue -f
or
postfix flush

Delete messages selectively:

mailq | tail +2 | awk 'BEGIN { RS = "" } / falko@example\.com$/ { print $1 }' | tr -d '*!' | postsuper -d -