Can you post the complete text or post a screenshot of the alert.
Is this MS Outlook (not express) ?
This looks like a heuristic detection and that should have also indicated why it was suspicious (not potentially a virus), the Heuristic settings can be modified, etc.
What is the sensitivity setting of either Internet Mail (outlook express) or Outlook/Exchange (MS Outlook) ?
If you can answer the above hopefully someone else wil pick up on this as I'm about to call it a night, almost 2 a.m. here.