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I'm dealing with a properly updated 'bird: 140.5.0 (32-bit) running on an equally updated Windows 10 desktop. First thing this morning, out of nowhere, I started getting an "unable to write the email to the mailbox..." message when sending, thus I could send but not save. And then I realized I wasn't receiving either, on all three accounts in my Thunderbird. I stopped everything and focused on trying to fix this. It's been an all-day, losing effort. So far.

I tried the various quick checks and fixes recommended here and there: I'm running the program as an administrator. I restarted the program. I rebooted the computer. I think I have enough disk space, but to be sure I deleted some bloat from possibly overly large files. I compacted, even though the program is configured to do that regularly. I temporarily disabled my antivirus program. I went into my webmail and deleted all messages that have arrived since my Thunderbird stopped receiving, in case one of them was corrupted. And probably some other attempts as well. Nothing has helped.

And now a second, even worse issue has fallen from the sky. Thunderbird opens. The folder list is where it always has been. The number of unopened messages in each folder is there in boldface, as always, but...the folders are all blank and I get the dreaded popup: "unable to open the summary file...." Have I lost my years' worth of carefully curated emails?

I've tried folder repair. I've deleted parent.lock. Etc. Nothing. Nothing. Nothing.

I will be super-grateful for any wisdom sent my way.

I have been using Mozilla Thunderbird for decades and they have even contributed a small amount of money to Thunderbird periodically. Just within the last two or three days all of a sudden I have been unable to send emails with my phone. I receive emails, but I do not send them.

So I opened up a laptop where I did not have Thunderbird and set it up properly through Spectrum using the incoming and outgoing servers as mail.twc.com. and yes, just like on my phone. I continue to receive new emails, but even with the laptop I was unable to send an email.

I received the message"send message error sending a message failed. The message could not be sent because the connection to outgoing server smtp mail.twc.com was lost in the middle of the transaction. Try again."

I contacted Spectrum twice and both times they had me try to send a message through their Web server spectrum.net and that message did go through. Of course then their response is that this has to be a problem with the third-party app meaning Mozilla Thunderbird, and they can’t help with that at all. I sure would appreciate some help because I hate to walk away from Thunderbird as well as change my email address after all of these decades.

I have been using Thunderbird with two POP3 Hotmail accounts for some time and I am trying to set up a third account with exactly the same configuration. However, both the automatic and the manual configurations failed. The new account receives mail, but the outgoing smtp server config seems to have a problem. Sending messages times out or keeps prompting for a new password.

The Hotmail account has POP3 and IMAP enabled. Thunderbird is set to receive all cookies. I cleared history and cache after every attempt and also temporarily disabled the firewall.

Any suggestions about what the problem could be?

My old email server was Mediacom (mchsi.com). I had that email account plus a gmail account on Thunderbird. Sometimes people said their emails to my gmail account would bounce. I changed email servers and no longer have the mchsi.com email or Mediacom server and have 2 gmail accounts on Thunderbird. The new one works fine. When I send an email to the old gmail account it bounces back saying "address not found. Your message wasn't delivered to ------@mchsi.com because the address could not be found or is unable to receive mail. 550 5.1.1 I had the tech that sold me the PC look at the settings on Thunderbird for the gmail account and he said they were okay. Where else can he check? Somehow the pc thinks that just that one gmail account is run through or attached to mchsi.com Kathy foggiak@gmail.com

Something horrible and time-consuming has changed within this past week to Thunderbird. My version is 140.7 1esr 64bit. Over the past 4 days or so, I've found I cannot scroll down and see the full emails--until I have to use this new pop-up system.

This is definitely not an improvement in my estimation. Is there any way to undo this?

Two nights ago I uninstalled ExpressVPN from my system at the instruction of one of their "support" people. My computer immediately lost the ability to access half of the websites I tried to visit and Thunderbird wouldn't send or receive email. I rebooted and that fixed every issue, but since then, Thunderbird no longer checks for new messages for any of my accounts. If I manually instruct it to check, it downloads the messages with no problem. I don't use any add-ons, and I'm using the latest version on a Windows 11 PC. I have already tried deleting global-messages-db.sqlite, repairing each mail folder from within Thunderbird, clearing the cache, and running an install of the latest version. I have also tried changing the setting for each mail folder to alter the interval for message checks by a minute just to see if that would jog it, but no luck. I've looked at various other help threads for this and am out of ideas. Thanks in advance for any help.

Cannot send messages. I get an error code:

Sending of the message failed. An error occurred while sending mail: Outgoing server (SMTP) error. The server responded: RBL restriction: Blacklisted by Internal Reputation Service - 73.62.119.4.

This is a recent abberation. I've updated to the latest version of TBird. But cannot understand this message or why I get it. Please help as I forward/send many messages daily.

Thank you

I quite often get this message, though it tends not to be a problem later "Unable to write the email to the mailbox. Make sure the file system allows you write privileges, and you have enough disk space to copy the mailbox"

One of the solutions seems to be Compact a File. How do I do this?

I have multiple accounts in Thunderbird. I use Unified Folders for inbox. If I click "New Message" while in the Unified Folders view, the message will send from my default account, which is bill@billbauman.com. But, if I want to change my send from account to bill@ntur.ai, where I have a signature configured, the image in the signature fails to load. But, if I change my focus to select the inbox for bill@ntur.ai and click "New Message", the default send from account is now bill@ntur.ai, and the image in the signature loads just fine.

The image is publicly hosted and loads fine in any browser: https://images.int.dreamhosters.ai/account-482257/ceb3563cdab64978.jpg

I tried to make this as simple as possible for debugging, so I change the signature to just the image. Here is the code: <title>Email Signature</title>

I am running Thunderbird 147.0.2 (64-bit) on Windows 11.

I can make a screen recording demonstrating the behavior.

Does anyone have a solution for this?

Thanks all in advance!

I have Mozilla Thunderbird email application with Windows 11. Recently I have problems opening some email texts, but not all. I do receive the mails and heading, but the contents are not displayed. This goes for some mails, and I do not see any connection as to which ones open and which ones don't. I would appreciate your advise. Bo Dahlberg

On my PC Thunderbirds sending/receiving mail says the mail server refused my connection. My laptop works fine. I have duplicated my laptops in/out specifications onto the PC but still nothing works. Spectrum says everything on their end is fine but can't vouch for roadrunner who is the rr in my mail address of ca.rr.com. All this started about 4 days ago. Any ideas on what to try next? Thanks.

Why suddenly has Thunderbird stopped logging my messages that I filter manually even though I have logging enabled? It used to work just fine. It no longer logs ANY message filtering. I have not changed any settings. I depend on it especially to confirm that new filters I set are working properly. How can i fix this?

I have just acquired a replacement PC and installed Thunderbird, and (as happened on previous occasions) I am unable to send emails because the outgoing server settings that were automatically detected are incorrect, and even feeding in those I recorded on the last occasion does not work. I have had a long conversation with somebody at Plusnet Help Desk, who agrees that the outgoing server should be mail.care4free.net and the port number should be 25, and the connection type should be SSL. He also thought that on my "Account settings" screen there should be an option "Account actions" through which I may be able to solve the problem, but this is not there. I think that last time I had this problem, some genius on this forum managed to solve it, and hope that this will again be the case!

Good morning,

I have a Thunderbird desktop client connected to an email on a Smartermail server via IMAP. Receiving mail just fine, but sent mail stalled on the send then gives the following error.

Your message was sent but a copy was not placed in your sent folder (Sent Items) due to network or file access errors. You can retry or save the message locally to Local Folders/Sent Items-chrissy@fruitacoop.com.

I can switch it to save to a local sent folder, but that is not a viable permanent solution. I have searched and followed all suggested troubleshooting steps I could find in the community forums without success.

Steps tried: - completely removed the account and added it back - completely removed Thunderbird and all app data, reinstalled - Tried many suggested "copies and folders" configurations

All unsuccessful. If anyone has had this issue and has any insight into a soluution, I would be forever grateful.

Can get(POP3), but can not send emails to a newly created personal outlook.com account.

the following error occurs when trying to send mail: Unable to authenticate to Outgoing server (SMTP) . Please check the password and verify the 'Authentication method' in 'Account Settings | Outgoing server (SMTP)

all my setting are correct per thunderbird and microsoft:

  (smtp-mail.outlook.com, port 587,  STARTTLS, OAUTH2, xxxxx@outlook.com)

thunderbird error log file contains the following: . . . mailnews.smtp: S: 535 5.7.139 Authentication unsuccessful, SmtpClientAuthentication is disabled for the Mailbox. Visit https://aka.ms/smtp_auth_disabled for more information. [CH5P220CA0005.NAMP220.PROD.OUTLOOK.COM 2026-02-28T23:29:21.878Z 08DE7703D4D1982A]

SmtpClient.sys.mjs:452:17 mailnews.smtp: Command failed: 535 Authentication unsuccessful, SmtpClientAuthentication is disabled for the Mailbox. Visit https://aka.ms/smtp_auth_disabled for more information. [CH5P220CA0005.NAMP220.PROD.OUTLOOK.COM 2026-02-28T23:29:21.878Z 08DE7703D4D1982A]; currentAction=_actionAUTH_XOAUTH2 SmtpClient.sys.mjs:578:19 mailnews.smtp: Error during AUTH XOAUTH2, sending empty response . . .

Based on my understanding its seems thunderbird is using SMTP AUTH instead of OAUTH2 as required for newer personal outlook.com accounts. Is my assessment correct? If so, is there a fix?

i am crying here i have changed my password for Comcast several times but i think ih ave screwed up The smtp server i am not sure wast do do there this is what i have can yu please tell me what to do please help i t will not et me send please

Hey there. Hope you're all doing just fine.

TL;DR Tried moving all my email messages from GMail to Infomaniak. Worked fine because I can see all my old GMail messages now on my Infomaniak Inbox using Thunderbird on my PC. But my phone refuses to show me the latest messages. It only shows me messages from 2025. --- Now with a lot more detail. I use Thunderbird as my email client of choice on both my Android phone and on my Linux (Manjaro) PC. TB on the PC is running 140.8.1esr 64 bit flatpak installed. TB on my phone reads 16.1 and has been installed from the github repository using Obtainium. I use IMAP for receiving and SMTP for sending. No POP3.

I have two email accounts. One at GMail and another at Infomaniak. Up until recently, I've only had the GMail account set up on both my phone and PC. I've been using Infomaniak as webmail just for testing. But recently I've decided to add Infomaniak's to both my Thunderbirds and move all my emails from GMail to Infomaniak. I used Google Takeout to download the mbox files (inbox, archive and sent), then using my PC I loaded the mbox files in my "Local Files" and finally I moved the messages to my Infomaniak correct IMAP folders.

It all looks just fine in my Linux PC. But on my phone I can only see messages from 2025 on my inbox. And I have many messages from 2026. I can see them using TB on my PC, or via the webmail. They just won't show on my phone.

EDIT: It only shows me messages from 2025 and prior to that. But it doesn't show me all messages from 2025. Many messages from 2025 are also missing. And from previous years too. This is not happening on the inbox folder only. It is also happening on all the other folders too. It's as if TB was filtering the messages. It's driving me nuts.

I've already tried clearing TB's data and import my settings. Still only have messages from 2025. What could be going on with Tbird on my phone?? Thanks in advance. Cheers