Error code 5.7.1 authentication required?

I'm using mac book but using emails to come by using outlook mac 2011 and i use to receive and send and now all it does is give me an error code 5.7.1.authentication required also its a business account ania@redhillre.com under araffone@yahoo.com its ridiculous i pay for domain yearly and i can't send emails show more I'm using mac book but using emails to come by using outlook mac 2011 and i use to receive and send and now all it does is give me an error code 5.7.1.authentication required also its a business account
ania@redhillre.com under araffone@yahoo.com

its ridiculous i pay for domain yearly and i can't send emails