How to change SMTP server IP (Exim IP) on WHM server

1) Login to WHM
Click Exim Configuration Editor
Check the box next to:
“Send outgoing mail from the ip that matches the domain name in /etc/mailips (*: IP can be added to the file to change the main outgoing interface)”
Save Changes
Then edit the file /etc/mailips
from shell and add:
*: #ReplacewithnewIP#
service exim restart
2) Login to Shell
Access the Exim configuration file:
nano /etc/exim.conf
Locate remote_smtp
The default setup will look like:
remote_smtp:
driver = smtp
interface = ${if exists {/etc/mailips}{${lookup{$sender_address_domain}lsearch{/etc/mailips}{$value}{}}}{}}
helo_data = ${if exists {/etc/mailhelo}{${lookup{$sender_address_domain}lsearch{/etc/mailhelo}{$value}{$primary_hostname}}}{$primary_ho stname}}
Change to:
remote_smtp:
driver = smtp
interface = 12.14.12.14 # Change to your server IP address.
Save changes and exit.
Restart Exim
If there is an exim update when you upgrade your cPanel server you will need to re-enter the interface again.

source  : https://kb.hivelocity.net/how-to-change-smtp-server-ip-exim-ip-on-whm-server/