sbcglobal.net is an att (legacy) domain. If you set up as POP then you cannot simply swap the pop account to an imap (or vis versa) by just changing settings - you would need to remove the pop account and then create new account as IMAP. So make sure all is removed and restart Thunderbird, so then you can start afresh. '''Regarding the password:''' You cannot not use the regular password which you use to access webmail. AT&T have stopped this and now require you to use a secure mail key. You have to create a 'Secure mail key' - see info at link below: https://www.att.com/support/article/email-support/KM1240308 So when you are creating the account in Thunderbird: when it says enter password - you enter the secure mail key Make sure to select the checkbox to remember password before you click on 'Continue' Thunderbird should find the correct settings, but I've included them below just in case you need them. Note: it is likely that Thunderbird will default to the 'Imap' settings, so if you do not want that option then you will need to click on the 'stop' button, carefully make changes, click on 'Re Test' button then click on 'Done'. Otherwise let it use the configuration settings it locates and click on Create account. '''POP3 ''' * server name: inbound.att.net * Port: 995 * Connection SEcurity: SSL/TLS * Authentication Method: Normal Password * User name: full email address. * SMTP outgoing server name: outbound.att.net * Port: 465 * Connection SEcurity: SSL/TLS * Authentication Method: Normal Password * User name: full email address. '''IMAP ''' * server name: imap.mail.att.net * Port: 993 * Connection SEcurity: SSL/TLS * Authentication Method: Normal Password * User name: full email address. * SMTP outgoing server name: smtp.mail.att.net * Port: 587 * Connection SEcurity: STARTTLS * Authentication Method: Normal Password * User name: full email address. This link tells you what server settings to use: https://www.att.com/support/article/dsl-high-speed/KM1010523/