How do I count the messages of Postfix's mailq?

I use this:

mailq | grep -c "^[A-F0-9]"

You can pipe the output of mailq through various other filters such as uniq, sort and wc to get other statistics.

either mailq | tail -n 1 or find /var/spool/postfix/deferred -type f | wc -l

both works