qmail and its 30 second delay.
the installation of nagios left me stumped in one area. i realized that running check_smtp in /usr/local/nagios/libexec/ kept taking exactly 30 seconds before it worked, and since the check_smtp executable gives a CRITICAL - Socket timeout after 10 seconds, it was pretty essential to get it confirmed as working within that 10 second period.
this issue only seems to plague users of plesk.
the trick is actually to edit the following file:
# vi /etc/xinetd.d/smtp_psa
it is necessary to add -R right after the server_args directive.
e.g.: server_args = -R /usr/sbin/rblsmtpd -r [snip]
then, simply restart xinetd.
# /sbin/service xinetd restart
now, on your remote nagios box, try it:
$ /usr/local/nagios/libexec/check_smtp -H 192.168.0.1
the response time should be instantaneous:
SMTP OK - 0.113 sec. response time|time=0.112892s;;;0.000000
now, only if check_mysql compiled correctly on my server, i'd really have all my bases covered!