[exim] High capacity and simplicity for Exim

Hello All,

I'm am trying to determine the best setup for the following scenario,
and even wonder if Exim can do some of this:

master_server.com (just an example) contains the email campaign software
which is accessed by different companies for creating their different
email campaigns.

I don't want CompanyA's sender reputation to influence CompanyB's sender
reputation and so forth and so on down the line. Yet, all companies
must access the same master_server.com and all companies have the option
of specifying different smtp settings for outgoing mail.

Knowing that which, in your professional opinion, would result in higher
throughput and greater efficiency with Exim (remember, there may be high
load times when tens of thousands of messags are outbound):

1) Have Exim reside as an smtp server on master_server.com and based on
the email header or other bit of information contained in the outgoing
emails, route the emails to specific company's external smtp server for
relaying the message to the appropriate user in different domains,
(that's if the user does not specify within the software what external
smtp server to use) or;

2) Let the campaign creators specify their own external smpt servers
(which the campaign software will let them do) and leave it at that for
the outgoing messages.

I thought that there may be some benefit to having exim reside on the
master_server.com server in terms of overhead and efficiency.

I am open to any and all suggestions.

Thank you.