Mail from my IMAP account is marked "delete" as soon as I open it.

[mac'n'wintel]

All,
New to Outlook so my apologies... I've configured an account on Outlook to
successfully receive (and sync) my IMAP mail account on .mac (yes, am an
Apple boy)... it all works ok except as soon as I open a new mail item it is
marked as delete (with a line thru it). I do not wish this to happen, of
course.

I have no rules set up (in Options) and anything else funky that might be
imposing this event.

Any help appreciated...