Go to the KeyChain application and delete all passwords for servers associated with that account. In Mail, check that all settings are correct. Reinput the passwrod information in the preferences. You will get a prompt when checking and sending mail and just save the passwords again in KeyChain.
Are you using POP or IMAP settings? Here are the pop3 settings:
Email Program Settings Field: | Enter: |
Incoming (POP) | inbound.att.net |
Outgoing (SMTP) | outbound.att.net (requires authentication) |
Incoming mail server: | POP3 |
Incoming/Outgoing User Name: | Full AT&T email address, including domain (e.g., test@att.net, test@bellsouth.net) |
Incoming mail port #: | 995, secure connection (SSL) checked |
Outgoing mail port # | 465, secure connection (SSL) checked |
In addition, this happens on occasion to me using ATTs email addresses. Probably has trouble getting to the servers on occasion. I just usually close the message box and try again it it goes through. If it happens constantly, then that's a problem.