I've been using the mail program on my macbook for a long while now and never had any problems. All of a sudden today I'm getting this message when I try to send anything:
The server response was: Authentication required
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.
Sending from: Bree Eagle <firstname.lastname@example.org>
I don't know what has happened or how to fix it. Help!!