[exim] Relaying confusion

Hello All,

I'm new to Exim4 and have chosen it because of the scope of an upcoming
job. I could use some advice.

We have chosen to go with Exim4 because it scales much better and has
great tuning capacity and can be fine tuned.

This will be a multi-company email campaign that will perhaps handle
upwards of 1 million email messages per month from several different
domains/companies as an example: 123.com, 456.com and 789.com. Now,
having said that, I have what will be undoubtedly a couple of newbie
questions:

All email campaigners will login to the same master server from which
they compose their campaigns, as an example, master.com. The master.com
only handles email message composition software, not smtp software.

I do not want all emails, however to be identified as coming from the
same Exim4 smtp server because there is a potential that senders from
123.com, for example, may develop bad sender reputations and I don't
want that to slow up the deliveries of emails to the campaigns for the
456 and 789.com's.

Given that speed and overhead need to be fast what are the
recommendations from this group about the network setup? Should each
sender have their very own Exim4 server that they identify in their
outgoing emails, or can 1 Exim4 server serve messages for all companies
but nevertheless have a setting which can be tweaked to identify
messages from 123.com as IP yyy.yyy.yyy.yyy and from 456.com as being
from IP zzz.zzz.zzz.zzz, etc?



Thanks so much for advice.