Saving Email

Got a question;

I'm using Thunderbird as my email client with no issues on an Intel IMac
with OSX10.4.11

I purchased an email backup pro program that I'm using for email backup.
This gives me a complete email restore for everything, but the file
isn't accessible of course so the saved email can be seen.

Is there in existence a program that allows you to archive email so that
it can be referenced and read if necessary on a backup media?

In other words, what I'd like to do is transfer each month's mail from
my sent and archive folder to off system media, then delete those
folders and start clean with them again.
My archive folder alone has 145 megs of mail in it, and even compressed,
that's a lot and it's building.
The problem is not having a program I can archive mail to off the system.
Has anyone addressed this issue and perhaps have some suggestions?

Everyone please note I'll be reading every response. I deeply appreciate
your time and thank you all very much for your help.


--
Dudley Henriques