imap backups
A friend of mine was asking me the other day how to best archive his email. I recommended Thunderbird and IMAP to her, so I was the natural one to ask.
I had never given this much thought before since I also run the servers where my email sits (and run the backups there as well). So I browsed around a bit and found IMAPSize (Windows only) which seems to do the job nicely. It even offers incremental backups of accounts.
It's free, but you can paypal the developer.