for some reason I can not reply to an email in my outlook unless it is another cox account. I can send and receive but I can't reply.

I can not reply to email unless they have a cox email address. I can send and receive anything but I can not reply to any other address except for cox. Please help!  Error Message is : System Administrator   Server error: '550 5.1.1 <xxxxxxx@gmail.com> relaying not allowed'

Terri