[exim] Rotating SMTP Outgoing IP addresses - SOLUTION

I'll just throw this out there for anyone else who need to search for a
simple way to do rotating IP addresses. This example assumes you have 10
IP addresses that you've dedicated to outgoing email and the idea is to
get about an equal distribution so as to get past rate limiting on the
receiving side. In this example we are rotating from 65.49.42.0 to
65.49.42.9

interface = 65.49.42.6${eval:${substr{-2}{1}{$tod_zulu}}%10}