Cant send emails in Outlook XP

[Madmax2001]

I am running Outlook XP on my machine and connecting to the email servers through a wireless connection. I can receive emails perfectly fine. However when I try and send emails Norton does not even get to scan the email for viruses and I just get an error report saying:
Your message did not reach some or all of the intended recipients.

Subject:
Sent: 01/11/2003 19:18

The following recipient(s) could not be reached:

_____@hotmail.com' on 01/11/2003 19:18
550 Administrative prohibition

When I test the accout setting a mail is sent and scanned using norton. Can anyone shed any light on this problem?

Thanks in advance