The fact that the same accounts work on a different computer tells us the problem is specific to your Thunderbird installation or your computer's security settings. The program is getting stuck trying to get past the initial connection.

Check Your Antivirus and Firewall

This is the most frequent cause of this issue. Your security software may be intercepting or blocking Thunderbird's connection, causing it to freeze.

Temporarily Disable. Try briefly disabling your antivirus and firewall, and then restart Thunderbird to see if it can connect.

Create an Exception. If the connection works with the antivirus off, you need to go into your security software's settings and find a way to add an exception or "whitelist" for the Thunderbird application. This will allow it to communicate freely without being blocked.

Disabling AVG anti virus doesn't help. No firewall that I know of. Connection to internet is "use system proxy settings". Been that way for more than 10 years.

This computer was turned off for a week as I was out of town.

When I turned it on yesterday, I got the described "freeze".

Pressing the "get mail" button briefly shows "connecting to inbound.att.net" then "connected to inbound.att.net".

Just had a similar issue and it turned out that while away with everything turned off it had decided to change the incoming server settings! changed them back and all now fine

Wish it was that simple. Checked server settings and they have not changed. Re-entered them just to make sure. No luck.

1. Check Your Computer's Date and Time

If your computer was off for a week, its internal clock might be slightly out of sync. Look at the clock in the bottom right-hand corner of your screen. Make sure the date, time, and year are completely accurate.

2. Repair the Incoming Mail Folder

Your computer is able to connect to the server, but it seems to get stuck right before downloading messages. This often happens if the local index file for your email folder gets corrupted.

In the left-hand panel of Thunderbird, right-click on your email inbox. From the menu, select Properties. Click the "Repair Folder" button. This will rebuild the folder's index. Restart Thunderbird and see if it can now download mail.

3. Change Your Server Security Settings

Even though your settings have worked for years, your email provider (AT&T) may have recently updated the security protocol on their server. Your Thunderbird installation may need to be updated to match.

Go to Tools > Account Settings. On the left, select Server Settings under your AT&T email account. Look for the setting that says Connection Security. If it is set to SSL/TLS, try changing it to STARTTLS. If it is already set to STARTTLS, try changing it to SSL/TLS.

Click OK and restart Thunderbird.

Time and date are correct. "Repair Folder" button pressed. 100+ messages changed from read to unread. Mark them as read and repair folder again. More or less the same messages come up as unread.????????

All of these are for messages prior to 9/5/2025, the last time computer was on.

Connection security was SSL/TLS. Changed to STARTTLS.

Message" Looked for inbound.att.net" shows for several seconds then. goes away. Does not get mail.

Changed back to SSL/TLS and get "Connected to inbound.att.net" Stuck there again.

The behavior you've described with the "Repair Folder" button—repeatedly changing messages from read to unread—is a very strong sign that the local file that tracks your inbox's messages has become corrupted.

Even though Thunderbird can connect to the server, it gets stuck because the corrupted file prevents it from properly indexing or downloading new messages.

The next step is to force Thunderbird to rebuild that file from scratch, which should fix the "stuck" status.

1 Locate Your Mail Folder Open Thunderbird. Go to Help > More Troubleshooting Information. In the Application Basics section, find the Profile Folder row and click "Open Folder". This will open a new window showing your profile folder.

2 Delete the Corrupted Index File Inside your profile folder, navigate to ImapMail. Inside ImapMail, you will find a folder for your AT&T account (e.g., inbound.att.net). Open it. Inside your account folder, find the file named Inbox.msf. This is the corrupted index file.

Completely close Thunderbird.

Delete the Inbox.msf file. Deleting this file is safe. Your actual emails are stored on the server, and Thunderbird will rebuild the file from the server the next time you start it.

3 Restart Thunderbird After deleting the Inbox.msf file, open Thunderbird again. When Thunderbird starts, it will be forced to re-download all the message headers from the server to rebuild the inbox index.

This process may take a while if you have a lot of messages, but it should fix the "stuck" status and allow you to get new mail.

Interesting. There is an inbox.msf, inbox-1.msf and inbox-2.msf All have a modified date of 5/17/24

Would the inbox.msf be the one to delete and ignore the others?

The multiple .msf files means that Thunderbird has created backup copies or temporary files for your inbox.

The file you should delete is the main one inbox.msf.

The other files, inbox-1.msf and inbox-2.msf, are older versions or temporary files and are not the ones currently being used by Thunderbird. Deleting only inbox.msf is the safest and most effective way to force Thunderbird to build a new, clean index from your server.

Remember to completely close Thunderbird before you delete the file.

Well, that didn't work. Still stuck on connected to inbound.att.net