If you are running your or your clients are running their own private exchange server in the office and need an external mail server set up from the cPanel server pointing to your exchange server then you will need to follow those steps below
Go into WHM / DNS Functions / Edit a DNS Zone
choose the domain > where it says
mail | 14400 | cname | domainname.com
change to
mail | 14400 | A | 111.111.111.111 ( which is the IP of your customers preferred mail server)
This will point the system to the new mail server !
and then log into your server using SSH as root
Remove the domain from /etc/localdomains
nano /etc/localdomains
and put the domain into /etc/remotedomains
nano /etc/remotedomains
to find an MX record :
dig domainname.com MX
