Rob wrote:

A simple solution is to set both machines to leave messages on
server. Email Accounts, Internet settings, Advance Tab. This way if
you open a machine and download the email and then open the next
machine it will still be able to download the same email.

Naturally, this doesn't address any issues of sharing of contact or calendar
data, but since the OP didn't ask for that, it may not be an issue and this
suggestion will be fine. Of course, this suggestion is not "sharing" in any
way.
--
Brian Tillman