Needs a lot of work to be useful on CentOS

I’m on CentOS and it seems that mailstats works pretty differently on CentOS than FreeBSD (What the author wrote it for).
I had to re-write a large part of the script… I also gave it the ability to check for warning and critical values for received and sent mail, something else lacking here. I spent probably 4 hours bringing this script up to a usable point for us.