Official documentation :
https://documentation.cpanel.net/display/CKB/How+to+Configure+the+Exim+Outgoing+IP+Address
The /etc/mailips file controls the IP address from which each domain sends mail.
To change specific domain outgoing email IP simply
[root@cpanel ~]# cat /etc/mailips
*: 111.222.222.112
domain.com: 111.222.222.112
domain.net: 111.222.222.113
domain.my: 111.222.222.113
domain.org: 111.222.222.114
vi /etc/mailipsRestart the exim service
service exim restart