I have a workstation running Windows XP Sp2, Outlook 2003, Firefox. Outlook has two accounts created. Both can receive - and send to any address except one. No filters have been set up. I deleted the contact and re-entered it. I can send to any other address - just not that one. What gives?

What error messages are you getting when you try ?

It gives me the error: "Unknown Error: Sending reported error 0x80040201"

Check here: 'Unknown error 0x80040201' - Tech Support Guy Forums

Thanks - already been to that link - and tried all the tips there - no luck. It took me a while to realize it is only not sending to one particular address - it is a correct address - until the last week it always sent to that address... just not now. Everything else ends...