Email archicing solution

Hi,

I was looking on Google and freshmeat.net for something to archive emails (lets say more than years old) for all users and move them somewhere - different file system.
I can't find anything free or able to do the job.
I'm going to write a script which will just move emails based on mtime and the tar/bzip them but that means manual process to retrieve emails when needed.

So what are you using to keep maildirs clean? Do you remove old emails? Do you compress emails?

Many thanks!
Chris