Thunderbird Community Forum

Sending of the message failed. An error occurred while sending mail. The mail server responded: <anonymous@[10.0.0.31]>: Sender address rejected: not owned by user a1.914306843. Please check the message recipient "christine.krieger@a1.net" and try again.

why do I get this on new download

As of September 3, 2026 all my new emails are going into a random folder instead of the inbox. This is also happening on my wife's PC plus and we are not getting the emails to our iPhones until we get out of Thunderbird. What has changed? This has not happened before.

I've been using Thunderbird on Windows 10 since last year sometime. Currently I'm on version 151.0.1.

I've 4 x mailboxes here and since yesterday, 3 of them show me an unusual message when checking for emails. I tried attaching a screenshot but although the screenshot uploaded, I couldn't find a way to insert it here. But the message says Unable to write the email to the mailbox and asks me to check if I've write privileges (which I have) and to cheek the available disk space.(currently 101GB free).

The message is happening 2 or 3 times each day and lasts for about half an hour, then everything works fine again. Has anyone else seen this??

I installed Thunderbird on my new laptop, then imported the profile from my old laptop

The main screen has, under "Inbox", folders for Drafts, Sent, Trash, Archive and Spam, which are being used by the program

Folders for Drafts, Sent and Trash also appear under "Local Folders" (along with Outbox) and these aren't being used by the program.

How do I get rid of these duplicate folders? "Spam" had a delete option, so that was easy, but the others don't.

I tried the two suggestions for a previous "Duplicates" question but they didn't resolve things.

Thank you

hi, snap thunderbird 155.0-1 ubuntu 24.04 keeps asking for passwords of all email accounts after upgrading thunderbird. all passwords are correct and they were not changed. the issue started today after thunderbird was upgraded to 155.0-1. this new version seems to have touched on oauth: https://www.thunderbird.net/en-US/thunderbird/155.0/releasenotes/

What’s New

- S/MIME popup shows signature, digest, encryption algorithms and key sizes

- Default address book for manually added contacts configurable with mail.addr_book.add_item_default_uri

- Enterprise policy DisableQRExport can disable QR export

- OAuth add-ons can override built-in settings for selected domains and hostnames

- Manual account config streamlined with Exchange, Graph, and custom OAuth support

- Custom OAuth support for IMAP and SMTP servers

- PKCE and external browser fields added to custom OAuth settings

- Enterprise policy DisableExperimentalFeatures for disabling experimental features

any idea how to fix this? thanks

I have had Thunderbird from the time I acquired my Mac computer. This week it started to do something new. After a restart I opened Thunderbird. A box came up that says across the top System Integration. The cursor balloons, and hasn't stopped for the time I powered the computer, as least fifteen minutes. You know how the program icons are in a dock across the bottom. With other browsers open, hitting the Thunderbird icon doesn't bring its window into the forefront. This needs either a reset, or possibly a backup first. Is there a quicker way to fix this? Thanks in advance. I am not using a VPN; but I also have Thunderbird on my Windows 11. You might have seen a more recent thread on that installation. I included a screenshot. It was easier here to do that than on the Windows 11. On the Mac, I just had to use Activity Monitor to close out of Thunderbird in order to get its version.

Outlook.jpの個人アカウントをThunderbirdで使用しています。 IMAPは outlook.office365.com / 993 / SSL/TLS / OAuth2 で正常に受信できます。

SMTPは smtp-mail.outlook.com / 587 / STARTTLS / OAuth2 で送信すると、 535 Authentication unsuccessful, SmtpClientAuthentication is disabled for the Mailbox. と返されます。

smtp.office365.com / 587 / STARTTLS / OAuth2 も試しましたが、こちらは接続タイムアウトになりました。 MicrosoftアカウントのOAuth2認証と2段階認証は完了しています。 Outlook Web版・新しいOutlookでは送受信正常です。 Microsoftサポートには問い合わせましたが、Thunderbird側へ確認するよう案内されました。

この状態でThunderbird側にまだ確認すべき設定がありますか？ それともMicrosoft側でSMTP AUTHが無効になっている状態でしょうか？

Hello,

I am struggling to set up calendar and contacts sync between Thunderbird (v155@ubuntu26.04) and my google account. I use a university account to access google services, so my google account is not some.name@gmail.com but some.name@myuniversity.cz. I understand that Thunderbird somehow needs to invoke OAuth2 process with google, but I do not know, what to fill in the "Hostname" or "Location" fields for Contacts and Calendar, respectively. Any help? Thank you.

All of the incoming messages are going to Trash. This includes messages I have not indicated as trash. I get no new messages to my inbox. Started today, 09/04/2026.

Starting today (September 3), ALL of my received emails are being put into the Spam folder instead of the Inbox.

FYI, I have been running Thunderbird (TB) for years and have not recently set up any new filters.

I'm currently running Thunderbird 64-bit version 155.0 under Windows 11 Home version 25H2. I am also running Bitdefender Total Security, but I have turned off its Antispam function, both under my usual Standard User account and the Admin account.

I have tried:

1. Going into TB Settings|Privacy & Security|Spam and clicking on "Reset Training Data." 2. After closing TB, I deleted the training.dat file in my TB profile folder and restarted TB. 3. Right-clicked on my Inbox and Spam folders and clicked on "Repair Folder." 4. Exited TB, copied my profile folder to an external HD, uninstalled TB and reinstalled TB after downloading from the official download site. 5. Rebooted my PC.

None of these approaches has worked to solve my problem.

Thanks for any help you can give.

I have Thunderbird 155.0 installed and also, TBSync + Google-4-TbSync to synchronise contacts between TB and Google.

However, I have just realised it hasn't been working for several months and TBSync is no longer compatible.

Are there other tools/techniques available to sync the contacts with Google?

I have been using Thunderbird successfully on Windows for years now, as my email client for a PlusNet email account in the UK. In May 2026 Thunderbird suddenly disappeared, as if it had been uninstalled, but I have no idea why. I managed to reinstall it and rediscovered the server details needed to reconnect to my account and fortunately had a slightly old back up (from Nov 2025) of previously saved emails. This has worked OK now for about a month.

Today the same thing has happened again - The Thunderbird icon on my desktop does not connect to anything and has just turned into a white "blank page" icon.

I may be able to get the account back by doing the same tedious process again, but I am concerned that this may keep happening and I don't know why.

This is a work laptop running Windows 11 so its possible I suppose that some sort of security software may be doing this without notifying me?? I am using Thunderbird to access a personal (ie not work) email account so maybe my work systems don't like that? As mentioned, it has worked fine for years so I dont know where the problem lies but it is worrying and annoying.

PlusNet last year transferred all email accounts to another UK provider (Greenby) but that has worked OK and I cannot see how that would affect email client software.

BJ

Notification requests I would like Thunderbird to 1) notify me that I have received new email(s) even before I have opened Thunderbird. Partly by changing the icon on the taskbar and partly by playing a sound. And 2) also retrieve the emails that are there automatically when I open Thunderbird. Is that possible? How do I do that? K.r. /hans peter

After your upgrade I was unable to send messages. The incoming I was able to fix but the outgoing I could not fix. I have included the email message sent to me and I have included a picture of the outgoing STMP,

Since the last (v155) update, TBird started putting all incoming email into one subfolder under my main inbox. I have several message filters that sort incoming mail into various folders. When I disabled the message filter associated with the folder in question, the email started coming into my inbox folder again. The message filter connected to that folder has not been changed in a while, and is a "match any of the following" rule with a number of specific from/contains/[text] entries. When I examined the filter closely, I found two rules where the [text] field was blank, which apparently was causing the problem, but as I said, I haven't changed the filter in a while - what recent change might have caused this? (Either adding empty fields or else considering [blank] to be equivalent to [any].)

Most other email clients I've used have had a way to manually "expunge" a mailbox, i.e. delete the messages which are marked for deletion. This includes Thunderbird on a machine at home (I'm traveling right now).

On this laptop I'm using Thunderbird 102.12.0 on macOS 26.6.2. All of my mailboxes use IMAP. Thunderbird is using Maildir for local storage on this laptop, and I believe the same is true on the machine at home (also macOS 26.6.x, not sure of the exact Thunderbird version), but I won't be able to verify this until I get home tomorrow evening.

On both machines, when I delete a message, the message list shows that message with a line through it, corresponding to the IMAP "marked for deletion" flag. The same is true on the other email clients I've used over the years.

On the machine at home , when I right-click on an account's "Inbox" folder, there is a "Compress folder" option which expunges the deleted messages from the mailbox. This option is not present in Thunderbird on this laptop.

So my questions are ...

• Is the menu item I'm talking about, only present when the account uses MBOX for local storage, and maybe I missed a step when I created the account on the machine at home? (If so, I know how to fix that when I get home.)
• Every email client I remember using, all the way back to the original `pine` in the mid-1990's, has had an "expunge" command of some kind. Does Thunderbird really not have a way to manually expunge a mailbox? If so, this seems like a fundamental oversight on the part of the Mozilla developers.
• Or is there a way to do it, and my old eyes just aren't seeing it on the menus? (which is entirely possible)

Thanks.

(Side question, totally unrelated) ... why does the text entry control I'm typing this message into, have its own markup language instead of using standard Markdown? (And yes I am, at least in part, being old and gumbly here ... you kids get off my lawn!)

In the last couple of days I’ve had a couple of alerts from TB when in other apps, seemingly random times, but possibly when I get an email (from memory, about Thunderbird requiring access to my Google account). I haven’t received any emails for a couple of days and I can’t send them (connection to Outgoing server smtp.gmail.com timed out). But, in TB account settings an outgoing server test was successful (Successfully established a secure connection to smtp.gmail.com:465). I also can’t pause calendar reminders, whatever I do they stay on the screen (but I can delete them with the X in the top-right corner). I haven’t changed anything in my TB or Google account settings. I’ve checked authorisations in my google account and TB auth is there. On my (android) phone, I can send and receive emails OK. OS Name: Ubuntu 24.04.4 LTS OS Build: (null) OS Type: 64-bit GNOME Version: 46 Windowing System: Wayland Kernel Version: Linux 7.0.0-30-generic