Att.net Email sign in error for IMAP but its OK for POP3

Thanks for reaching us @w760a.

We understand your concern with regard to AT&T email. Let us help you stay signed in to your email.

Since you can access your email on your Samsung phone. Before you set up Thunderbird and in Mac OS, there is something digitally that needs to be done and that is to create a secure mail key.

Thunderbird is not one of the email clients that we actually support, we do not have a walkthrough that we could give you, but we do have the email server settings that are needing to be used. 

Since we have had you create a secure mail key, IMAP will be the server settings to use. Quick tip: Each time you have the password field just use the Secure Mail Key. 

Let us know how it goes. We're here to help!

Thank you.
David, AT&T Community Specialist.

Thank you for your response.  I'd like to better understand...without a secure mail key I am running my Samsung phone mail client, which is an IMAP setup.  So what is different between my phone and a desktop client such that I need a secure mail key?

Hello @w760a! Thank you for writing us back! We understand that when you use IMAP on Thunderbird mail client you're getting authentication fail error. We hear you, and are happy to assist you.

Please try removing the Thunderbird mail client and re-add it. Once you re-add mail client, please add the account details with correct IMAP settings present in our article about AT&T email server settings.

1. Check Your Settings:
   • Open Thunderbird.
   • Go to Tools > Account Settings.
   • Select your AT&T email account.
   • Verify the following settings:
     • Server Name: Use mail.bellsouth.net, or use the one in your email address (AT&T has many different domains present on the above provided article).
     • Port: Set it accordingly present on the above provided article.
     • User Name and Password: Make sure they are unchecked.
     • Connection Security: Set it to “None.”
   • Click OK to save the changes.
2. Authentication Method:
   • As you're using a IMAP mail settings, it is recommended to use Oauth2 as the authentication method that is the secure mail key.
3. Restart Thunderbird:
   • After making the changes, close and reopen Thunderbird to apply the settings.
4. Clear Cookies and Re-enter Password:
   • Open Thunderbird.
   • Go to Options > Privacy & Security.
   • Check the box to accept cookies (so OAuth authentication can complete).
   • Remove the passwords from Saved Passwords.
   • Restart Thunderbird.
   • When prompted, enter your account password in the OAuth window.

For more information, please visit our ⁠Email support page.

Let us know how it goes!

For further assistance we're here to help.

Thank you for contacting AT&T Community Forums!

Nate, AT&T Community Specialist.

That is what I tried, except for your recommendation to use Oauth2.  That is the config thar generates the authentication error on Thinderbird on my windows machine as well as IOS mail on my iMac.

I don't understand how using the recommended OAuth2 will address the authentication problem when it's fine without it on my Samsung Android phone.  The Imap config on my phone is working without Oauth2 set up.  

BTW,  POP3 is working on Thunderbird without any OAuth2.

Hi @w760a!

We hear you and want to help you with this. We would request you to check with thunderbird mail client support as this could be an application issue.

After reviewing your concern and trying to resolve through the Community Forums, it looks like you may need more account specific support.  To assist you best, we encourage you to review our Contact Us page to identify what method you’d prefer to reach out for this account level help.  You can call, chat, or reach out via social media, and we can review your specific issue and provide you support.  We’re sorry we weren’t able to resolve your concern directly in the forums, but let us know if we can assist with anything else.

Thanks for contacting AT&T Community and Forums.

Gary AT&T Community Specialist.