If you’re unlucky enough to be on Centos (I prefer Ubuntu), and you get the Postfix – Master is dead but pid file exists, error. Here’s how to fix it.
Rant: We only have a few clients on Centos because it’s just a constant headache.
You will need to remove sendmail as it conflicts. But, because Centos always has to make things harder, that will also remove cron. In our case, it didn’t remove the crontab file (with jobs), but back that up just in case.
yum remove sendmail #(it will want to remove cronie, cronie-noanacron, crontabs, sendmail-cf. Let it).
yum install postfix crontabs
It’s important to install them together or Centos will force other packages which will cause problems.