Postfix version:
# postconf mail_version
Postfix default settings:
# postconf -d
Postfix non-default settings:
# postconf -n
Delete one message with the named queue ID from default queues:
incoming, active and deferred
# postsuper -d queue-id
Delete all messages from the queues:
# postsuper -d ALL
Flush the mail queue:
# postfix flush