That fixed it--thanks! Despite not *really* having an Outlook inbox, I DID recently temporarily create one to adjust AutoSsync settings (to prevent AutoSync from gobbling up all of my battery).
For the record, the following fixed the problem:
Within the Mail tab...
(1) select Inbox (in the lower left) -->
(2) click Inbox dropdown (in the upper left) -->
(3) expand the "Outlook E-mail" branch -->
(4) should see a (1) in its inbox--delete and voila!