You can follow these steps to change Exim Mail IP of a server.
1.Login to cPanel as root. Then,
2.Main >> Service Configuration >> Exim Configuration Manager
Basic Editor >> Domain and IPs
change the following options as follows,
Send mail from account’s dedicated IP address off
Reference /etc/mailhelo for outgoing SMTP HELO on
Reference /etc/mailips for outgoing SMTP connections on
3.Login to server backend as root. Then,
4.Open /etc/mailhelo and add the following line in it.
*: <server_hostname>
Example: *: myserver.com
Example: *: myserver.com
*: <new_IP>
Example: *: 123.123.123.123
Reference:- You can use the following cpanel doc for reference.
http://docs.cpanel.net/twiki/bin/view/AllDocumentation/WHMDocs/EximDifferentIps
Notes:-
1.You can also give separate mail IP for each domain and subdomain
Example: /etc/mailips ----> example.com : 123.45.67.89
/etc/mailhelo---> example.com : example.com
sub1.example.com : example.com
sub2.example.com : example.com
addonexample.com: example.com
/etc/mailhelo---> example.com : example.com
sub1.example.com : example.com
sub2.example.com : example.com
addonexample.com: example.com
2.To check whether the Mail IP changed or not, just send a mail and view the mail header. You can view the sender mail IP there.
Reference:- You can use the following cpanel doc for reference.
http://docs.cpanel.net/twiki/bin/view/AllDocumentation/WHMDocs/EximDifferentIps