email error 5.1.0

[dawnzy2009]

I keep sendind a email to my friend through yahoo,this keeps coming back...can you tell me what it means?

5.1.0 uknown address error,550-5.1.1 th email adress,>. recepient adress rejected:user unknown in virtual alias address table

[jsconyers]

Welcome to the forums. Are you sure you're entering the email address in correctly? It doesn't appear as if you are.

Try sending to the exact same address from your PC and see if you get the same error.