I get this error message for only some of my outgoing email, others go Ok and I'm receiving emails OK.
"The reason for the problem:
5.1.0 - Unknown address error 550-"SC-004 (BLU004-MC1F18) Unfortunately, messages from 62.24.202.73 weren't sent. We recommend that you contact your Internet service provider. The problem is that too many unwanted messages have been sent from the following IP address above. You can also refer your provider to http://mail.live.com/mail/troubleshooting.aspx#errors
TalkTalk have been totally useless on this one!