"I noticed this bug when I tried to forward a mail from Hotmail to my office account, which came from a Hotmail user," Nadarajah wrote in an email interview. "It never reached me (I tried three times). Then I spent a whole night to find the actual problem."
The problem, it turned out, was that the email service was failing to forward messages originally sent between two Hotmail accounts to a third non-Hotmail address.
But a page on the free Web-based service was confirming that messages were forwarded when they hadn't gone anywhere.
Microsoft today said it had patched the bug.