A couple of things need to happen if you are not hosting email on the server.
1. Remove example.com from /etc/mail/local-host-names 
To do this SSH into the server. 
su - root
cd /etc/mail
vi local-host-names 

2. You might also need to delete the coolantexpress related entries in the /etc/mail/virtusertable
and run vnewvirtmaps
To do this SSH into the server. 
su - root
cd /etc/mail
vi virtusertable
vnewvirtmaps

see source

host email off server linux commands

email, Bash, linux

Bash