Thunderbird Community Forum

Hello Thunderbird Support Team,

I am experiencing serious email problems with Thunderbird on two Windows 11 computers.

I use Thunderbird for approximately 12–13 email accounts, mostly Gmail accounts, for my accounting work.

• • The main problem:**

Thunderbird receives incoming emails, but I cannot send messages from multiple accounts.

On the first computer, Thunderbird displays the following error:

"Sending of the message failed. The connection to the outgoing server (SMTP) smtp.gmail.com timed out."

On the second computer, Thunderbird repeatedly asks me to authenticate my Gmail accounts again. The authentication process does not seem to resolve the sending issue.

• • What I have already checked:**

- Thunderbird version: 153.6.0 ESR on the first computer. - SMTP server: smtp.gmail.com. - Port 465 with SSL/TLS and OAuth2. - Tested port 587 with STARTTLS – same problem. - Thunderbird successfully establishes a secure connection to smtp.gmail.com:465, but sending emails still fails. - Cookies, including third-party cookies, are enabled. - Tested Thunderbird Troubleshoot Mode. - Restarted Thunderbird and Windows. - The problem occurs on two different computers and different Wi-Fi networks. - Gmail accounts work through the web browser.

• • Additional information:**

The problems initially appeared when one Gmail account stopped synchronizing. I removed that account from Thunderbird, but its IMAP server configuration remained in the Thunderbird profile (prefs.js).

I subsequently experienced sending problems with other accounts.

I found Bugzilla report 2062925, which appears to describe similar problems involving multiple Gmail accounts and SMTP timeouts.

• • My questions:**

1. Is this a known issue in Thunderbird 153 ESR? 2. Could a malfunctioning Gmail account or an orphaned IMAP configuration interfere with SMTP sending from other accounts? 3. Is there an official fix or workaround that does not require deleting and reconfiguring all accounts? 4. Could Google OAuth2 authentication or Google Contacts synchronization be responsible?

I would appreciate your help. I rely on Thunderbird for my daily accounting work, and I cannot currently send emails reliably.

Thank you in advance.

Thunderbird

Configuration

• Windows 10 Desktop
• Multiple Email accounts managed by Thunderbird
• Functioning "normal" for multiple years

Problem

• One of the email accounts has been put together as almost a clearing account where all of my other emails are auto-forwarded from the email to the inbox of the account in question.

* Recently this account has stopped accepting emails either by auto transfer or by cutting and pasting emails into the inbox and also by cutting and pasting from a folder within that email account to the inbox.
   

Identified Issues

       When looking at the account settings, I noticed that the account in question with the input issue also, next to the account name, has a mustard-yellow-colored star that none of the other accounts have. I don't see anywhere in Help, Technical, or whatever any meaning for what that means. That's where I think the problem lies. 
   Potential Solutions
       As a workaround I have started forwarding emails from one email into The account in question as a clearing account this clearing account. That involves taking an account from Gmail (as an example) and forwarding it to a folder that specifically is for input from Gmail ... but then the filters don't always work because they're not going through the input box. 
       Do you have any suggestions or fixes that I should be aware of and try? 

	Thunderbird Version 	153.6.0esr   Build ID 	20261026222624

I had a number of emails that were labelled 'unread'. I pulled down the command that was tagged to only show unread emails. I touched every email that was unread to get a clean plate. Since all emails were now read, I got a blank screen; all. How do I get my emails back. I can not remember what tools I used, or where the tools came from. I have over 6K emails, but I can not get at them. Please help. George

My two Optimum email accounts (POP3) stopped sending messages. See attached error message. They are still working on a different computer with the exact same settings and Thunderbird version (Windows 10 on both too). I also have Outlook and Gmail accounts all still sending fine. Sending from troubleshooting mode and clearing the startup cache didn't help. Any clues what I can try?

When a task is set up one of the options is to prioritize the task. However, the saved task is not sortable by priority or searchabe by priorty and doesn't show its priority when in a list, I have to wonder why it is there if it doesn't add any related functionality.

I have Thunderbird on Linux Mint Cinnamon

Hello,

I'm very fond of Thunderbird (using it only for agenda, but a lot) and I think that a new practical function would be to be able to paste plain text (= without formatting) with the right click of the mouse into an agenda cell.

As I add a lot of events and text into the agenda cells directly from websites or documents, I'm always getting the original formatting that I don't need and can look quite bizarre.

Plain text could harmonize everything. I know I could select the text and reformat it in Thunderbird but it's adding unnecessary steps.

Thanks in advance for the consideration of my proposal, thank you developers, and have a good day !

I currently have spectrum service and have gone through this with them. Everything is fine on their end. TB is throwing this message when I try to send an email.

"Sending of the message failed. The message could not be sent because connecting to Outgoing server (SMTP) mail.twc.com failed. The server may be unavailable or is refusing SMTP connections. Please verify that your Outgoing server (SMTP) settings are correct and try again."

It all worked fine until last week.... Once this started, I changed all servers / ports etc to the settings Spectrum suggested to no avail.

Any ideas?

I sent email, email goes out from thuderbird but copy is not saved is "sent mails", its only for one receiver, for all other it works, why? before it work for this receiver too

i am migrating from Outlook to Thunderbird and cannot see how i can migrate my tasks: i have trawled the internet but can only find out-of-date info about old versions of TB or using 3rd party tools: how can i sync TB tasks with Outlook or at least import tasks from Outlook for access in TB?

Hello, I am experiencing repeated freezes in Thunderbird 153 ESR on Windows 10. I have been investigating this problem since mid-October 2026, but have not been able to identify the cause. Thunderbird is essential for my daily work, so I would appreciate advice on identifying the cause and restoring stable operation.

1. System environment - PC: dynabook R63/B - OS: Windows 10, 64-bit - Thunderbird: 153.6.0esr, 64-bit - Mail provider: @nifty (Japan) - Incoming mail: POP3 over SSL/TLS, port 995 - Security software: Super Security (Japanese security software) - Mail storage: Local mbox files

2. When the problem started Thunderbird worked reasonably well until September 2026. The freezing problem began around mid-October 2026. Windows Reliability Monitor recorded Thunderbird as "Stopped responding" on October 19, 2026, at 9:48 a.m. This is the earliest recorded incident I have found, although the problem may have started earlier. Thunderbird update history: - September 18: 153.3.1esr - October 1: 153.4.0esr - October 14: 153.5.0esr - October 21: 153.5.1esr - October 28: 153.6.0esr The first recorded freeze occurred after the update to 153.5.0esr. However, I have not established that the update caused the problem.

3. Symptoms Thunderbird becomes unresponsive and usually has to be forcibly terminated. During these freezes, Windows Task Manager often shows Thunderbird using approximately 30–40% CPU, repeatedly around 39–40%. Freezes also occur when Thunderbird is using only about 1.1 GB of memory. On other occasions, memory usage has increased to approximately 2.56 GB. The problem occurs under several different conditions: 1. During manual POP3 mail retrieval. 2. After repeated manual mail retrieval operations. 3. Approximately 30 minutes after a single mail retrieval, even when Thunderbird is left idle. 4. Sometimes after replying to messages or copying messages to other folders. 5. In both normal mode and Troubleshoot Mode. 6. Sometimes during the first mail retrieval after starting Thunderbird. Other Windows applications generally remain responsive when Thunderbird freezes. Restarting Windows sometimes restores normal Thunderbird operation temporarily, but the problem returns.

4. Troubleshooting already performed I have already tried the following: - Reinstalled Thunderbird from the official website. - Created a new Thunderbird test profile. - Disabled extensions. - Disabled hardware acceleration. - Disabled global search and indexing. - Removed all active Thunderbird message filters for testing. - Disabled the anti-spam component of Super Security. - Disabled automatic mail checking and automatic downloading. - Tested manual mail retrieval in Troubleshoot Mode. - Reduced the size of the Inbox from approximately 4.1 GB to 2.4 GB. - Performed a full antivirus scan, which detected no threats. The new profile initially worked, including several successful POP3 retrievals, but the freezing problem later returned. Reinstalling Thunderbird did not resolve the issue. The anti-spam component remains disabled for testing, but the problem continues.

5. Windows error records Windows Reliability Monitor recorded Thunderbird as unresponsive on October 19, 2026, at 9:48 a.m. Windows Event Viewer also recorded an Application Hang, Event ID 1002, on October 30, 2026, at approximately 4:23 a.m. The affected executable was thunderbird.exe, version 153.6.0.0. These records confirm the application hang but do not identify its underlying cause.

6. POP3 communication Earlier POP3 logging confirmed that Thunderbird connected to the @nifty POP3 server and received a CAPA response. However, I have not identified which POP3 or internal Thunderbird operation was active at the exact moment of the freeze. I have not collected a process memory dump.

7. Potentially related Mozilla bug reports I found two reports that may be relevant: - Bug 2080699: POP mail retrieval becomes unresponsive in Thunderbird 153.4.0esr. - Bug 2031744: Freezing potentially related to mail index (.msf) files and background processing. Some symptoms are similar, but I cannot determine whether they have the same underlying cause.

8. Questions I would appreciate advice on the following: 1. Are there known POP3-related freezes or high-CPU problems in Thunderbird 153 ESR, particularly after the October 2026 updates? 2. Could background mail processing, folder maintenance, or mail index files explain a freeze that occurs while Thunderbird is idle? 3. Could interaction with antivirus software or Windows networking components cause these symptoms? 4. Are there diagnostic steps that can help identify the cause without repeatedly freezing Thunderbird or risking existing mail data? 5. Would this information be more appropriate as an additional comment on an existing Bugzilla report or as a separate bug report? I have already spent considerable time testing different configurations. I would prefer to avoid repeating tests that have not helped. I have a backup of my Thunderbird profile and would like to preserve my existing mail data.

Thank you for your assistance.

Hello ! Thunderbird is runing on Mint Linux. There is a Email account on Austria A1 (Telekom) This account has primary a number such as aon.999999999@aon.at and you can make an alias on it just as "your_name@aon.at". Tihs account has been reading with thunderbird for 2 Years. now A1 has posted, they have to change the number. So they did but the alias has stayed the same. Before this I have made 3 local Archives with thunderbird named 2024, 2025 und 2026 in which I transfered the elder Emails I wanted to keep. After the Change from A1 the local Archives still can be seen by their names but when you klick on them you dont see any Email. What can I do to get them back ? I had a look at the dataset where the data are stored, and in Editor I still find the Emails, but not in thunderbird. thank you for your advice - and sorry for my poor english. grretings from Austria

For various reasons related to password confusion I decided to delete an existing gmail account from Thunderbird 153.6.0esr 32-bit. I then tried to open it again using the existing email address (having done this many times before with no problem).

But I get stuck at this stage as I am waiting for a popup and nothing comes. I've tried deleting history and cookies, changing browsers, checking OAuth2, etc as suggested in various places, but still I get this spinning wheel going on and on.

Any suggestions?

tl;dr: I'd like to argue that a user who executes the archive action has seen the email in question, and that executing this action means that the email is no longer "newly downloaded" and doesn't deserve the highest of visual markings anymore.

We're not talking about the read/unread bit here (the green dot and the grey numbers in the folder pane). We're talking about the "newly downloaded" aka. "new and unseen" bit (the yellow star/rhombus and the blue numbers in the folder pane).

When a new email arrives, it's marked as "newly downloaded" and the inbox lights up blue because of it. Fair enough. It's also unread, of course. I often archive emails right away without opening/reading them. But I have seen the subject line of course, and I have a pretty good idea of what the email is and why I don't read it. I have the message pane disabled, so I can easily select an email without it being displayed and being marked as read. In the past, I used the message pane combined with that "mark as read after 1min" setting.

Now when I archive the message, the archive folder lights up blue and when I go in there, the email that I just archived has a star/rhombus. But I don't want my archive folder to look interesting with a blue color only because I just moved an email into it. All the blue colors are supposed to be for things I haven't seen yet and still need to look at. In fact, any email I move to a place should not be able to make that place look blue. Blue color should be for things that appeared for other reasons.

I'm aware that switching folders (e.g. away from inbox and back to it) or restarting Thunderbird will clear this "newly downloaded" bit. But I'm not doing that. I stay in the inbox, I get emails, I read them or archive them immediately. And when a folder on the left lights up in blue (that can happen thanks to my filter rules), then I take a look at that one as well. My Thunderbird application runs for weeks.

In an answer to a previous question, I learned that Spectrum email has issues. I have since learned that Spectrum is slowly phasing their email out. So I'm guessing that change is necessary for me. If I create a free Outlook account on my W11 desktop, is using Thunderbird still an option? This whole email thing is confusing for me. Thanks for any help.

After upgrading from the previous ESR series (140.17.0esr) I can no longer access my mailbox, due to the OAuth2 authentication process failing.

As to items on https://support.mozilla.org/en-US/kb/thunderbird-and-yahoo: 1, 2, 4, and 5 I have double- and triple-checked. 3 is unclear to me: I'm unaware of anything hidden, yet at the same time I would have expected the site to ask me for a 2nd verification step (e.g. sending a numeric token to my mobile phone) after having entered my password. Whether that step isn't shown or whether the failure (see attached picture) occurs ahead of this I cannot tell.

Needless to say that this occurs at about the worst of all possible times, where I will need my private email much more because of soon losing my business one.

Hi,

For both servers imap.exmail.qq.com / imap.263.net, when I click on the email subject in the email list during downloading processes (many emails headers are being downloaded but email body downloading is not completed), the email is broken without any content (only header).

I go to the web email server and move the email to another folder and then move it back to inbox. Then I delete the same email in Thunderbird and donwload again the email again, it's completely downloaded with the email body.

I don't have any issue with eM client or Outlook for such issues. Any possible setting to solve this issue?

Thanks.

I currently get my email from Spectrum.net. They have made some changes that necessitates me making server changes in Thunderbird. I can't seem to find a way to do that. Everything seems to point me to a new account. If I set up a new account will I lose all of my eisting emails on my desktop?

In thunderbird I'm getting the "Help Keep Thunderbird Alive" page, when I click the link it opens the same page (https://updates.thunderbird.net/en-US/thunderbird/140.0/nov25c/donate/?form=nov25&utm_content=cta_c&utm_source=in_app&utm_medium=desktop&utm_campaign=nov25_appeal) in the browser. The click to donate button there just opens the same page again and there's no option to donate. The page has a notification that "an extension might be blocking our donation platform" but disabling ublock on the page does not change anything.

Do you have a working donation page anywhere?

About a week or so ago my Win11 laptop stopped downloading my emails reliably. When I open Thunderbird it goes to the server and then to the server inbox and then closes down. This happens most of the time. Occasionally it randomly will download all of the emails accumulated that it had not downloaded before although I haven't done anything differently that I'm aware of. I use Network Solutions to host the email server. I called Network Solutions and they could see nothing wrong. The only thing I see that was not happening before is that I am getting an inordinate number of threat Mcafee popups that I can't seem to stop. I don't know if this has anything to do with it. This has been incredibly frustrating because I don't know what to do. Any help is more than appreciated! It says Thunderbird is up to date and I think the version is 153.6.0esr(64Bit)