Select a different outgoing mail server from the list below or click Try Later to leave the message in your Outbox until it can be sent. The server response was: Authentication Required. The sender address was rejected by the server. i've just tried to send an email now and get this error message: All I had to do was add account and sign in with my google info.
In the apple store the sales guy set up gmail through the apple mail program, but we didn't actually check it. Just brought home my first mac ever, macbook pro 13' retina.