Changing Exim's Sending IP

Anyone running a shared hosting server is probably now accustomed to dealing with constant complaints about blacklisting. It's exim's default setup on a cPanel server to use the shared IP of the server to send email, which means that all your clients on one server are sending out email on the same IP.  All it takes is for one spammer to send out a mailing list or one customer to get hacked and run a Darkmailer script, and suddenly everyone on your server seems to be complaining about getting their mail bounced.

You can change the server's IP address for sending email. Assuming you already have an IP set up on your server with a valid PTR, you probably already saw on the cPanel forums or some other location that you can simply change the interface lines in your /etc/exim.conf file and restart exim:
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_hostname}}
dk_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_hostname}}
dk_private_key = "/var/cpanel/domain_keys/private/${dk_domain}"
dk_canon = nofws
dk_selector = default
In the above example, all you'd do is comment out the interface lines and replace them with:
interface = xx.xx.xx.xx
However, this tends to be a band-aid fix, as a cPanel update or any change made in WHM's Exim Configuration Editor will regenerate the Exim config and overwrite your change. To make this more permanent, you'll want to use the /etc/mailips file.
To set this up initially, go into WHM > Exim Configuration and enable this option:
<
code>** 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) [?]
Or, in /etc/exim.conf.localopts, add/change this line:
per_domain_mailips=1
Then run

/scripts/buildeximconf
service exim restart

*The /etc/mailips file should be root:exim, chmod 440  if it doesn't already exist.

chattr +i /etc/mailips

Now for actually changing the IP:

Changing the IP Globally

If you want everyone on the server to send out on the same IP, just add the following to /etc/mailips:
*: xxx.xxx.xxx.xxx
Then add the IP and it's matching PTR to /etc/mail_reverse_dns:
xxx.xxx.xxx.xxx hostname.tld
This will tell Exim to use that IP for any sender on the server.

Changing the IP Per Domain

If you want your users with dedicated IP addresses to be able to use those IPs to send email as well, you can add them to /etc/mailips. cPanel actually now has documentation on how to do this properly:
http://docs.cpanel.net/twiki/bin/view/AllDocumentation/WHMDocs/EximDifferentIps
If you have multiple dedicated IP domains already, I've devised a simple loop you can use to populate /etc/mailips automatically:
while read line ; do DOMAIN=`echo -e $line |awk '{print $2}'` && IP=`echo -e $line |awk '{print $1}' |cut -d: -f1` && echo "$DOMAIN: $IP" >> /etc/mailips ;done < /etc/domainips
You'll always want the wildcard line to be in there to account for any domain not listed in the file, whether it is the main server's IP or another that you have assigned for email:
*: xxx.xxx.xxx.xxx
Then:

cp /etc/domainips /etc/mail_reverse_dns

This will set all the existing sites on dedicated IPs to send out mail on those IPs.