Thus said Josh Smith on Sun, 19 Dec 2010 08:07:45 EST:

quoted text
> Weather or  not I keep  it in mbox format  or convert it  to something
> else - what sort  of tools are out there to break  it up into multiple
> archives by year or perhaps sender?

There's mbox2maildir  out there. You  might also look at  mail/mairix in
ports.

Andy