Can't send email

[Bob]

I have been using Outlook to send email for some time.
Suddenly it won't send.

I get this message "Task 'pop-server.stny.rr.com Sending
and Receiving' reported error 0x800CC78 'unable to send
the message. Please verify the e-mail address in your
account properties.' The server responded ??05.7.1
Outbound mail refused - 66.24.254.213"

I have looked at my ISP's (Road Runner cable) help file
and can't find anything. I have checked my e-mail set
up, which seems ok, except that it says "e-mail send
test:failed".

Can anyone tell me what to do?
-Bob