Following are the steps you can follow to update or verify your ATT.net email settings.
Go to file > account settings.
Tap the AT&T email account and then tap Change.
Please enter the correct settings for IMAP and POP.
Enter the user's full name next.
Select the remember password checkbox and enter the secure mail key in the password field.
Next, Outlook will test your account settings.
Tap on close, then finish.
Verify or update AT&T email settings
Already have your email set up, but want to update your email account with your secure mail key? Here’s what you have to do:
Select File > Account Settings.
Choose your AT&T email account and then select Change.
Confirm or enter the following IMAP or POP settings:
Incoming server: imap.mail.att.net (IMAP) or inbound.att.net (POP3)
Outgoing mail server: smtp.mail.att.net (IMAP) or outbound.att.net (POP3)
Check or enter your User Name (full AT&T email address).
In the password field, enter your secure mail key and select the Remember password checkbox.
Select Next. Outlook will test your account settings.
Select Close, then Finish.