I'd like to change my mail server configuration but don't know where to start. Would appreciate any guidance.

Currently my mail server is my web server. On my pc (linux/mandriva) I run thunderbird, which downloads email from my web/mail server to my pc. Same thing with a couple other user computers.

I'd like to set up a mail server in my home office (actually, piggy back on an existing server). But I'd like that mail server to be the final repository for all mail - not just the incoming, but so that mail is no longer kept on my local pc.

I believe the advantages to this are that I would be backing up all email, current and past, from the server. In addition I can then connect to that mail server remotely/offsite and everything stays synced.

I think I need to:
1) set up my mandriva server as a mail server.
2) somehow move my existing mail files from my pc to the new mail server.
3) setup my pc so that it no longer 'downloads' the emails, but instead operates remotely to send/delete/manage emails on the webserver.

Any guidance on what I need to do to go through these steps?