Mac Mail

Mac Mail keeps giving me this message when click on newly received emails in my inbox.

The message from john doe <john_doe@yahoo.co.uk> concerning “Re: ” has not been downloaded from the server. You need to take this account online in order to download it.

However my status is online, and my internet is working fine as well.

I am using a Powerbook G4 400mhz w/ 768 Ram
on Mac OS X 10.3.9.
and
Mac Mail 1.3.11 (v622/624)

I tried rebuilding the mail box several times and that seems to work for a few hours or so....but then eventually it gives me this message again.


any suggestions? It is really annoying to have to close mac mail every time I want to read new mails.