We had a problem with the nagios check_mailq plugin at work, it kept timing out. So I wrote a simple bash script (instead of 610 lines of perl) which is “compatible” with check_mailq (supports the same arguments) which uses “exim4” and is very quick. Just drop it in /usr/local/bin/check_mailq_simple.sh and adjust your nagios conf to use that instead of check_mailq