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One of my two outlook email accounts no longer appears in Thunderbird, which says it is authenticated but not connected. This happened suddenly. I can still get the messages by going onto outlook.com. How do I get it back on Thunderbird?

Hello everyone,

We are currently investigating an issue where browsers are sending HTTP requests with Connection: close in the header during integrated Windows authentication (NTLM authentication) via SAML Service Provider (SP), leading to premature termination of the TCP connection.

This behavior occurs in the middle of the authentication process, preventing the NTLM authentication from completing and subsequently prompting for re-authentication.

We have observed the following browser behaviors:

Chrome and Edge: These browsers function without issues, communicating with Connection: keep-alive. Safari (macOS): Older versions of macOS with Safari exhibit the Connection: close behavior, leading to authentication failure. Newer versions of macOS with Safari work correctly with Connection: keep-alive. Firefox (macOS): Even on the latest versions of macOS, Firefox continues to attach Connection: close, resulting in authentication failure. Upon reviewing logs, we've identified that various browsers attach the Connection: close header during the NTLMSSP_NEGOTIATE request in the NTLM authentication sequence. Although this happens in an environment with a load balancer, we have confirmed that the load balancer is not modifying the header; rather, the client (browser) is adding it.

We would appreciate your insights into the conditions under which Firefox attaches Connection: close to HTTP requests, especially considering the differences across macOS versions and other browsers, addressing the following points:

Are there any known conditions or past cases where Firefox outputs Connection: close in an NTLM authentication environment via SAML SP? Given that older Safari versions show similar behavior, we are also considering if there's a common factor depending on NTLM authentication and browser version. What are the general heuristics, logic, or triggers for a browser to decide to "close" a connection or to attach Connection: close? We are particularly interested in cases that occur mid-authentication process. Could specific configurations (e.g., the combination of SAML and NTLM authentication, or the presence of an intermediate proxy/load balancer) potentially influence Firefox's Connection: close behavior? Are there any additional logs or debugging information we should collect from the Firefox client side to further pinpoint this issue? Any guidance or suggestions you could provide to help us resolve this problem would be greatly appreciated.

Thank you.

I am using the Thunderbird software (140.7.1esr 64-bit) for mail merge purposes on a Windows 11 operating system. However, when I start the mail merge process, it begins initially but then automatically disconnects before completing the task.

Due to this issue, I am unable to complete the mail merge properly. Kindly look into this problem and provide a solution as soon as possible.

Thank you.

I was using MS outlook and recently I could not connect. Apparently ATT made a change so that instead of a password you need a Secure email Key. Since I needed to make a change I thought I'd try Thunderbird mail, but I still need the KEY. After a number of efforts with the ATT AI and human support people I could not find where the Key is entered on ATT. Now I know this forum is about Thunderbird and not ATT, but there must be Thunderbird users that have ATT and have made a seccussful connection. There are a few ATT help pages that outline how to do this, but each time I look at my ATT profile I can not find where to enter the Secure Mail Key. Is there anyone that can help me with this? THanks Mike

I received this message: Unable to connect

The connection was refused when attempting to contact localhost.

   The site could be temporarily unavailable or too busy. Try again in a few moments.
   If you are unable to load any pages, check your computer’s network connection.
   If your computer or network is protected by a firewall or proxy, make sure that Thunderbird is permitted to access the web.

I am not receiving new email. What do I need to do to get it working again?

I've been using Thunderbird since it was first made available for Android, and I've used it successfully until recently. I have a new Outlook email address that I cannot sign into even though the Outlook email I have been using with Thunderbird since the beginning has never given me any issues. I get the "user authenticated but not connected" error. What can I do to resolve this issue so that I can have all my emails together in one app. Just to make things clear my old Outlook account which uses the email in writing you from connects flawlessly. It's a new one that is giving me issues. Any help would be greatly appreciated. Thank you for your time.

I’m using Thunderbird to connect my Hotmail account. The setup shows as “successfully added,” but an error message appears:

“The operation on Inbox did not succeed. The mail server for account responded: User is authenticated but not connected.”

Previously, the connection worked perfectly, but starting this week, Thunderbird can no longer access or sync the hotmail mailbox.

How to fix this problem!!???

In Thunderbird account setup, I correctly enter my email account, name and password. I know it works because I can open my email on the Spectrum login page. I get a confirmation green box then when I press done a yellow box says unable to login at server, probably wrong configuration, username or password.

Hi! I hope you are well. It's my first time trying Thunderbird. I have the Linux Mint app. (seems to be the latest version available from the Linux Mint app store)

I attempt to sign into my Outlook.com email address on Thunderbird.

When I type my Outlook email and password and click Done, Thunderbird says configuration found in Mozilla ISP Database and it tries to pop up a browser window. Some website like login.microsoftonline.com is in the URL bar, but the browser window closes immediately without displaying a page.

Thunderbird say authentication failed. Either the entered credentials are incorrect or a separate username is required for logging in."

What do you think about the cause of this issue? Is this possibly an issue with my Outlook account or the Linux Mint version of Thunderbird?

I found a similar issue mentioned from a few years ago:[https://www.reddit.com/r/hyprland/comments/17q16cg/thunderbird_authentication_window_is/ https://www.reddit.com/r/hyprland/comments/17q16cg/thunderbird_authentication_window_is/ ] Where they used Linux and Thunderbird would open and close the Outlook window without giving a chance to login to the Outlook account.

On my computer, I tried: type a yahoo address into Thunderbird and click done and it opens a Yahoo website login window. So Yahoo seems to work, Outlook doesn't. Outlook's login window disappears by itself.

I was wondering if you have any suggestions for me? Is this the wrong place to report bugs (if you think its a bug)? (The Thunderbird app takes me to this place when I click Help > Share Ideas and Feedback.

Thanks so much for your time. :-)

Thunderbird info: Thunderbird for Linux Mint mint-001 - 1.0 140.8.0esr (64-bit) Linux Mint 22.3 - Cinnamon 64-bit

Hi all,

everytime I open Thunderbird I get a popup window from Yahoo finance with a server timeout message. I am unable to connect to get my emails through. I need to log on directly to Yahoo mail, which is a pain.

Hopefully someone can help me with this.

Find attached the popup image.

Regards

I have a new laptop with windows 11 (previously had a computer with windows 10) I got Thurderbird onto my new laptop however when I try to get in emails it keeps asking me for a new password. I keep entering the password for my provider but it does not remember it or does not accept itl It says its trying to connect to server but never does. then after a while it says it timed out. Is there another password I should be using?

Hi, Since up-date of Thunderbird on 02/25/2026, there is no more links nor update in my google agenda in thunderbird ( 148.0 realesed ). ?? Have you got any solutions? Regards

I have spent most of two days trying to Thunderbird to send email. It has worked perfectly for years. Suddenly, emails end up in Sent folder but go nowhere. My email host service sees nothing wrong. I can send emails through webmail and usually through Outlook. I have spent most of the day getting coached by Copilot and I am quite sure I have all the settings the way that worked flawlessly until two weeks ago. Is Thunderbird just dead and I need to go to Outlook?

all the sights I've used for years will not open and will not work I can't even use them any more they work fine in other browsers don't know what you did but it is almost unusable

The connection was reset

The connection to the server was reset while the page was loading.

   The site could be temporarily unavailable or too busy. Try again in a few moments.
   If you are unable to load any pages, check your computer’s network connection.
   If your computer or network is protected by a firewall or proxy, make sure that Firefox is permitted to access the web.

What can I do to resolve this problem.....Problem loading page

Thunderbird Version 140.7.1esr, Build ID 20260123195141 User Agent Mozilla/5.0 (X11; Linux x86_64; rv:140.0) Gecko/20100101 OS Linux 6.1.0-33-amd64 #1 SMP PREEMPT_DYNAMIC Debian 6.1.133-1 (2025-04-10) OS Theme Xfce / Adwaita Application Binary /usr/lib/thunderbird/thunderbird-bin

Having a problem with an ATT POP account. TB stopped getting mail. After a minute and a half or so (wish it would time-out faster), I get a pop-up box in the top right of the screen that states: "Connection to server inbound.att.net timed out" and then quickly goes away.

Deleted passwords and cannot see where to create them again, as it never prompts me for new ones.

Thanks.