I am supporting an office that has roughly 50 PCs.

The e-mail client consist a mix of Outlook Express and Outlook 2000/2003/2007.

Currently the e-mails are saved locally on the PC.

My supervisor has asked me to come up and implement a plan to back up the
e-mails onto the server on a weekly basis.

My requirements:

-E-mails are backed up every week.
-E-mail backup data are kept for two weeks then the e-mail data can be
overridden with new backup e-mail data.
-The system must be automated as possible.
-The system must ensure the e-mails are backed up.

Any ideas as to how should I approach this?

Any third party back-up programs can do this?