Sounds like you're being blocked by a blacklist or something. Have you gone
to the link suggested by the error message?

"alastair" wrote in message
. ..
Hello,
I can no longer send email with Outlook 2003. I can receive just fine,
just can't send. This is the error message I get:
Task 'xxxxxxxxx's Mail - Sending' reported error (0x800CCC78) : 'Unable to
send the message. Please verify the e-mail address in your account
properties. The server responded: 550 69.181.249.87 blocked by
ldapu=rbl,dc=comcast,dc=net - 550 Message sending error. Please go to
http://www.comcast.net/help/faq/index.jsp?faq=SecuritySpam17867'
Can anyone help me out with this? Any help would be appreciated, thanks!