Cannot send mail from Mac Mail with sbcglobal account
I have an sbcglobal.net account, using a Mac with Mac Mail to send mail. Suddenly it won't.
According to Mail Connection Doctor, everything is logged in successfully on POP and SMTP servers without issues. But when I try and send something, it fails. I get the following error (personal info redacted):
The server response was: Requested mail action not taken: mailbox unavailable
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: XXXX<XXXX@sbcglobal.net>"
the Host name I'm using is smtp.mail.yahoo.com, the Username is my email address, and the PW is my normal PW, which is working fine when logging into my webmail page.
I can send fine from my alternate servers. I can send fine from my ATT mail webpage. But something has gone haywire with the Mac Mail connection, even though it SAYS the connection is fine. Unless this is not on my end and is a server issue. Please advise.