If your server are having multiple IP and you want to send each emails in different IP address. You can follow the steps given below. This is used to maintain the ip reputation. While doing this, please make sure that this is not used for spamming.
Open you exim config,
vi /etc/exim.conf
search for the line : interface =
replace this line with
interface = 192.168.0.1${eval:${substr{-2}{1}{$tod_zulu}}%7+1}
If your server is having ip's from 192.168.0.11 to 192.168.0.20 , you can use above line.
+1 is is the starting ip ie 192.168.0.1'1'
%9 is the incriment value ie 11(192.168.0.11) to how much. here it is 20 (192.168.0.20)
