My friend had some issue to send emails to particular domain email address and I went through the error message, says Remote host said: 550 5.7.1. URL(s) listed in

I followed the link to resolve the issue: and got more ideas. If your mail server has been blacklisted, some email you send may not be delivered. You can check in this web link: Hope it will help for you as well.

If the mail server is blacklisted you can remove using easy self-removal provided by