Mail App Quits


my mail application quits shortly after opened and (apparently) when it tries to access the internet.

OSX 10.3.5 1.5GHz PowerPC G4, Mail 1.3.9 (V619)

I open the Mail application, and it will come up in a given mailbox (SEND), then I select the MAILBOXES option, go to IN, do some actions (delete a mail, select another mailbox) and the application will quit and I will have an error notification box ("Mail has suddenly quit. Do you want to submit a bug report?").

Opening MAIL again (or after restart, or shutdown and start), the original mailbox (SEND then IN) shows the same deleted items (groundhog day?).

By turning airport off, or unplugging ethernet, the MAIL application will stay connected and allow work to be performed and that work is NOT forgotten next time computer is turned on or following a disconnect. Once airport turned on or ethernet cable connected, however, the MAIL application quits again.

What can I do to keep it connected? Any ideas on what is causing it? Could it be related to Microsoft Office Powerpoint program (with which I'm having problems: recipients, on a regular basis, can't open what I send them). the first failure occured shortly after sending such a powerpoint presentation.

Thanks for your assistance.