check_mailq_filter – an Icinga / Nagios postfix mail queue monitor with a filter (include or exclude mails matching a pattern).

So to exclude facebook mails from your monitor you may run:

check_mailq_filter.py -x '.*facebookmail.*'

While you’re here, have a look at pfqueue – a console tool for interactively viewing your postfix queue that’s a step up on postcat etc.