Take the 2-minute tour ×  I know this has to just be a lack of
my understanding but here's the problem.  We recently changed
DNS servers from to .2, so I went around to all 8 of my linux
servers and changed /etc/resolv.conf to reflect the change. Note
that they're all static, there's no DHCP involved.  After making
the change I can immediately test the results using nslookup and
dig, and it all looks good. I did a /etc/init.d/networking
restart - to restart the networking subsystem - and restarted
apache and postfix on each of the servers, just to be sure.  A
few days later I get a report stating on of our websites isn't
sending emails anymore. Perusing the logs I found that the
mod_php process couldn't resolve dns entries to send mail. After
beating my head on it for about 30 mins I rebooted the server
and everything returned to normal.  The next day on a different
server (using CentOS rather than our normal Ubuntu), I get a
report stating that emails aren't going through, and sure enough
looking at the logs