Super Interspire Server? Rotating IPs with PostFix

Hopefully if you came here looking how to do this - some of the wonderfully gracious veterans here could post a step by step explanation.

So I have a dedicated server running Linux.
I have Interspire Email Marketer.

The server has 13 IPs. I want to be able to rotate the IPs as the emails are being sent from IEM. After 1000 emails sent on one IP - rotate and switch to the next. With 13 IPs - of course after 13,000 emails are sent - back to the first IP and so on.

The step by step using Webmin would be appreciated - as well would any comments and insight with regards to using this method.

Create 13 sub domains, install IEM in each sub domain with unique IP.

You need Exim and must understand how to config it. If you cannot, you need someone.

1 FrontEnd = Where your software runs
1 LoadBalancer = get the emails from the frontend and pushes to frontservers
1-100 FrontServer = Sends the actual emails out

If I can ask to define some of these ideas to better help my pursuit:

Exim: A Mail Transfer Agent (MTA) for Unix. This is similar to SendMail (another Unix based MTA) which then means it is also similar to PostFix (an MTA that is similar to SendMail.)

Before I get into the other items - is Exim necessary compared to PostFix? Can the same concepts you propose be completed with PostFix or is there something special about Exim that makes it the better choice?

No on to your birdseye network layout:

Frontend (where your software runs): I am assuming this is the dedicated server and/or VPS where you run your mail software. (In my case - I'm asking about Interspire, correct?)

Continuing with my assumptions of this setup - the Frontend (server) will also need to have the Exim (or PostFix?) MTA running on it to push out the emails to the next level (the Load Balancer) - is this correct?

LoadBalancer: I am researching this to learn - and I found this link:

http://www.zytrax.com/books/dns/ch9/rr.html#mail

However - it almost may seem this is describing the load balancing of INCOMING mail? Is that correct?

I also found this PDF article that goes into a little more detail:

http://anonym.to/?http://www.barracudanetworks.com/ns/downloads/White_Papers/BarracudaNetworks_WP_Load_Balancing_Email_Using_DNS_MX_Records.pdf

The last paragraph on the last page leads me to believe that this can also be used for sending email. (And who knows - from the little I know yet - this setup could default load balancing for both sending and receiving.) Here's that paragraph:

'In order to avoid complications when using multiple A records, make sure to add PTR records for all A records. If the receiving email system does reverse look-ups, the PTR records for all the A records must point to mail.mydomain.com. If all the A records do not point to mail.mydomain.com, the receiving email system can detect a mismatch and may reject the email if this is part of its anti-spam algorithm.'

However - this is also a brochure from Barracuda 'Load Balancer.' So in your set up - Loan Balancer is in fact a separate piece of functioning software? Is this paid for or free open source in the Linux environment?

Finally - you have FrontServer (1-100- actually sends emails out). This is where the concept of how set up starts to elude me even more. But I think I get the concept. I have ANOTHER dedi server or VPS that is set up to actually send out the emails. So this makes me think. Does the FrontEnd only run the Load Balancer - then the load balancer directs the email to be sent across to the separate FrontServer(s) - and THEN the FrontServer(s) are what actually run the Exim or PostFix or SendMail or whatever MTA you are using?

Again - thanks for the 'food for thought.' It's helped me to start a path down researching that has lead to some good info I have learned thus far.

It will continued to be GREATLY appreciated for more clarity, definition, explanation and your all around gracious help.