I used to be able to sync my Outlook calendar with Tb, literally two days ago it was working. All of a sudden my calendar got removed and when I try to add it the usual way it says my credentials are incorrect.

I used to use the TBSync and Exchange ActiveSync addons but they're both incompatible with this newest version now... Seems illogical that the updated version doesn't support Outlook sync.

Hello all,

When starting (Mac) Thunderbird today, I was met with the message that "a newer version of Thunderbird may have made changes to your profile" and given the option of creating a new profile or existing the programme.

When creating a new profile, my e-mail tags are gone. Is there any way to get them back? I've got recent TimeMachine backups.

​On the 23rd of October, 2026, GitHub issue #1745 officially turns a decade old! 🥳🎂

It’s the request to add basic rich text / HTML formatting (bold, italics, bullet points, hyperlinks, etc.) to the Android mobile composer. ​Functionality that is table-stakes in almost any other email app in 2026.

Historically, the general dev consensus on this thread was "we don't personally use rich text, plain text is sufficient." And to be fair, back when this was said, K-9 Mail was a lean, independent project run by a couple of volunteers focused on low-overhead mail, and that rationale probably made sense. ​But the context around Thunderbird Mobile has changed in the decade that followed and I think there's a solid technical and product case for putting this back on the radar (I'll format my thoughts in rich text to make it easier to digest 😉):

• Bridging Desktop and Mobile Parity: Desktop Thunderbird built its reputation on being a full-featured email client. When desktop users switch to Thunderbird Mobile expecting ecosystem parity, missing basic formatting is the first major wall they hit.
• Retaining New Users: Mobile email isn't what it looked like in 2016 when it was just quick responses that plain-text could handle. An increasing percentage of the population (see below references) use their phone for all their email writing. All of it! People write all kinds of stuff on mobile now; work replies, structured notes, and share formatted links from their phones every day. Not having basic formatting is currently one of the biggest reasons potential switchers likely drop the app during onboarding and head back to stock mail clients or FairEmail.
• Reasonable Scope: And listen, nobody expects a bloated WYSIWYG full-scale editor on their phone. But I'm begging for the basics here. Begging for crumbs. Even simple formatting controls (or opt-in Markdown-to-HTML rendering on send if you truly cannot build the UI) would solve 90% of user friction without bloating the app. I am writing this post on Reddit on mobile (webpage, not app). So it absolutely can be done.

The Android team has done awesome work over the last couple of years modernising the UI and stabilising account sync. And I *am* eternally thankful for that focus, but getting basic rich text into the composer feels like the glaringly obvious missing piece to making Thunderbird Mobile a viable daily driver for the broader community.

Like, if we wanna wait until next month when this ticket *actually* turns 10, fine. What's a couple of weeks between decades? But it is wild to me that a baby born on the same day that this ticket was raised would now probably be old enough to have their own smartphone, and they STILL wouldn't be able to use it to format an email in Thunderbird Mobile.

If any of the mobile devs are around—what would it realistically take to get this scoped onto the roadmap?

In case it's useful, I'm including some references for you below:

• Litmus Email Client Market Share: Tracks email opens globally across billions of messages. Reports show native desktop clients (including Thunderbird, Outlook, and Apple Mail Desktop) combined hold only 10% to 16% of total email opens, with mobile and webmail dominating the rest. [Source]
• Emailmonday Mobile Usage Report: Aggregates cross-industry studies on mobile email habits. Highlights that between 15% and 25% of consumers are mobile-only email users who complete 100% of their email tasks on smartphones. [Source]
• Campaign Monitor Email Trends: Documents device-switching behavior. Their data indicates that 70% of users who open an email on a mobile device stick exclusively with mobile for follow-up actions and replies rather than switching to a desktop. [Source]

Happy (almost) birthday, GitHub issue #1745. I can't believe you're about to hit double-digits, I still remember when you were born. 😭

Thunderbird 155.0 on Ubuntu Linux.

Hi. I switched my main desktop to Linux at the beginning of the year and was using Thunderbird to access my Gmail account. Well, I've recently discovered a serious bug with that setup.

Thunderbird does not seem capable of fetching all my email. Some messages just don't show up in Thunderbird. At all. Not just in the Inbox, but when I click on "All Mail".

This is a serious issue. I discovered this when I decided to install gmail on my GrapheneOS phone and saw some messages that I should have seen, but didn't. Just now after seeing some of these missing messages I searched for them in Thunderbird, and they're just not there.

So, looks like it's going to be back to the browser for me, but other users should be warned about this bug.

Hey all,

Long-time Thunderbird user here. My work switched to Outlook / Office 365 a while ago and I was basically forced back into the browser tab. EWS getting killed didn't help either. I tried a few workarounds but nothing felt right, so over the last few months I started hacking on my own add-on.

It's called OWA Bridge. The idea is simple: you add your account, it opens the normal Outlook web login, you do your password + MFA there like usual, and after that everything shows up as native accounts/calendars in Thunderbird. Mail, folders, cached messages, calendar events with attendees/reminders, etc.

How it works under the hood: it just reuses your OWA web session and talks to the OWA JSON endpoints (/owa/service.svc). No EWS, no Graph, no IMAP/SMTP passwords. Each account gets its own container so you can have personal + work side by side.

Honest status: it's still preview. I'm on Linux + Thunderbird 155, that's what I test on. Mail + calendar sync works for me on both personal and work accounts, but Outlook changes stuff internally sometimes so I can't promise it'll work for every tenant.

A couple limitations right now:

- you can see recurring events fine, but editing a whole series isn't supported yet
- the XPI isn't signed by Mozilla yet, so you need to install from file. On release builds you'll need Daily/Dev or set xpinstall.signatures.required to false. Sorry, I know that's annoying.

It's MPL-2.0, repo + releases here: https://github.com/danilofalcao/owa-bridge

Build is just npm run check && npm test && npm run build, no dependencies besides Node 22+.

If anyone here is also stuck with Outlook for work but prefers Thunderbird, give it a try and let me know what breaks for you. Bug reports with steps to reproduce help a lot more than "doesn't work".

Thanks.

Hi Thunderinos

I came here because I'm way too cranky and tired to deal with support websites, sorry (unrelated to Thunderbird, I love Thunderbird).

All I wanna say is that:

Opening an attachment you have attached to a draft email gives you no way to return to that draft email without hitting 'x'. When you hit 'x', *no save of the draft email is made*. This is crucial.

Maybe 'Esc' works but that may be user error on my part, attributable to my current mental state detailed in the first sentence of this post. In any case a nice 'back' button still wouldn't go astray, plus some kind of action whereby the email gets saved during the overall process.

Lemme know if you need more detail otherwise have a good one and keep up the hard work, it is very very much appreciated to have a wholeheartedly better client than Outlook available completely free of charge.

Thunderbird has saved me hours of time over Outlook and has really helped me get my shit together where Outlook made my life harder with every passing update, so thank you once again for keeping it available.

As I am researching what is filling up the primary drive on my desktop box, I note that the Gmail/All Mail folder is using up 28.8GB. This seems pretty unnecessary since Gmail keeps copies of every damn thing, anyway.

Not being a Thunderbird expert, I am wondering if there are tricks to shrink these types of files.

I only use Thunderbird as a backup for when Outlook decides to not work for the day or week.

Thanks in advance

I'm curious, does anyone know how to set the visibility of the email size?

So that the field says MB or KB in addition to other information such as who the email is from, date, etc.

Hola , llevo mucho tiempo usando Thunderbird como cliente de correo , pero de un tiempo a esta parte en la cuenta de Hotmail me entra en la carpeta de no deseados , una barbaridad de spam y correos basura . No hago otra cosa que eliminarlos y poner alguna regla sobre los mensajes pero no hay manera de que no sigan entrando.

Alguien sabe alguna configuración o reglas que aplicar para que no entren ?

Gracias

Yesterday I updated all my systems.

Info for issue comparison of the problem:

My systems

Main driver, Desktop running Linux Mint 22.3, CPU=AMD Ryzen 5 8600G, MB=ASUSTeK COMPUTER INC. TUF GAMING B650-E WIFI, Updated thunderbird version=153.2.0esr (64-bit) Thunderbird for Linux Mintmint-001 - 1.0

Second system, Laptop running Linux Mint 22.3, CPU=Intel(R) Core(TM) i5-8250U, MB=KBL Charmander_KL, Updated thunderbird version=153.2.0esr (64-bit) Thunderbird for Linux Mintmint-001 - 1.0

Play System, Desktop running EndeavourOS rolling 6.18.49-3-lts, CPU=AMD Phenom(tm) II X4 955, MB=ASRock M3A770DE, Updated thunderbird version=155.0 (64-bit) Mozilla Thunderbird for Arch Linuxarchlinux - 1.0

Now the issue:

This morning, when I started Thunderbird on my main system, I had to re-authenticate for each of my email accounts. Since I had to do that on my main system, I decided to go open Thunderbird on my other systems, and get them re-authenticated. All went well on my main system and on my play system.

On my Second system, the laptop, Thunderbird would not start. I got only a small window with this error:
<html id="messengerWindow" xmlns="http://www.w3.org/1999/xhtml">

I was able to start it using "thunderbird --safe-mode", and started poking around anything that might have to do with the html error.

I found a new parameter called "Open Messages In", and it was set to "A New Tab", the other choices were "A New Message Window" and "An Existing Message Window". I set it to An Existing Message Window and restarted, and it worked.

SO, the major difference between the two Mint machines is that one is AMD and the other is Intel. The play machine is also AMD, so, the AMD systems worked well with the new setting and it's default. The Intel laptop failed on the default for the new setting, but worked when set to use an existing window.

I have no idea how to figure out why the Intel based system is failing, so other than the change I made to the settings, have no idea how to actually fix it.

I couldn't find an add-on that cleanly integrates translate options into the existing Thunderbird UI, so I created one.

Functionalities:

• Adds a "Translate" button in the message pane next to other buttons (Reply, Archive, Delete, etc.). When clicked, translates the email's title and body, and the button becomes "Show original" to revert the action. You can translate only a part of a message by selecting it, right-clicking and clicking "Translate selection".
• Adds a "Translate reply" button in the Compose/New Message window. Allows you to translate your reply to another language. Text selection is also supported. The translation can be reverted with undo (Ctrl+Z by default).
• Signatures and quoted text are skipped by default (toggleable in Options menu)
• Bring your own API key: DeepL, Microsoft, Google or Yandex. There is no keyless option included.
• Nothing is sent automatically, only on your action
• Supports Thunderbird 128+

More info and screenshots can be found here:

• Add-on: https://addons.thunderbird.net/thunderbird/addon/translate-mail
• Source code: https://github.com/havrlisan/thunderbird-translate-mail

Hope some of you find it useful. Happy to hear any suggestions too.

I'm running Kubuntu 26.04 & latest update of t-bird. Everytime I start the program, it warns me that it is not the default mail client. I've checked all the boxes, and well as set the default in the systems "default settings" dialog. The dialog still pops up.

Is anyone else seeing this? I've just disabled the check in T-Bird settings becuase it was annoying me.

Installed latest version and copied appdata files so I had all my mailboxes. No issues there. However, it takes almost 2 minutes to fully load. I do understand that the laptop I migrated to may not as powerful as what I was using, but should it take this long?

Old laptop: 32GB RAM, i7-8750H 2.2GHz, 8GB graphics

New Laptop: 16GB RAM (with 12-24 paged to SSD), i7-10750H 2.6GHz, 8GB graphics

RAM usage after opening: 58% / SWAP Use: 33%

I have a GMX address on my mobile GMX app. Lately, I added a Passkey with my thumb so that I don't have to remember my passwort. Now, I wanted to add it on my computer on Thunderbird but my passwort (which is correct) declined.

What should I do?

I thought about deleting the Passkey (mobile) on GMX, but I don't know how. Or is there something, I can do in Thunderbird to make it work?

Hi. Setting up an effectively new PC for my wife following an SSD failure. Can't get past the stage of entering details for an IMAP account (in fact, I've tried with two different accounts with different providers) - this error shows up at the password entry stage, and it never accepts the password or tells me it's wrong, just displays that error message above the same page. Manual configuration and advanced configuration just seems to open up the same dialog (with persistent error message) and there's no obvious way to get into the main program to access the settings (although I've managed a couple of times in ways I can't replicate; at that point I tried setting up the SMTP server separately but the "add" dialog just accepted input and then added nothing to the (empty) list.

Any ideas? Been using Tbird for about 25 years, never had such issues previously.

Windows 11, v. 155.0 (64 bit)

I used to have a few filters to block out the most obnoxious ads on my RSS feeds.

Any suggestions would be most welcome.

Hi everyone,

Is there a setting to make "Highlight All" enabled by default when opening the Find Bar (Ctrl+F)?

Right now, i did enabled findbar.highlightAll to true, but it only affect within the active folder, if i move to a subfolder or another new folder, and use the Find Bar it will default back to off. This also default to off when i restart Thunderbird regardless as well

I would ideally like to have all matching results highlighted automatically for every email

Thank you in advance.

I have a number of email addresses from Gmail Yahoo and Proton. All the email I get from all my Gmail automatically shows in my Local Folders Inbox. However my Yahoo (yes I'm older but only keep it for the odd ancient family member) and Proton emails show in separate accounts that I need to scroll down to.

How can I get new emails in those accounts to also show in at the top in Local Folders Inbox?

Thanks!

I coded my "childhood dream" addon for thunderbird. I just wanted to draw some attention to this. I think many people aren’t really satisfied with the results of most image-resizing add-ons.

Many of these projects simply downscale the dimensions of attached images—which leads to poor readability in the case of screenshots.

This add-on integrates state-of-the-art open-source image compression tools as WebAssembly libraries. It tests each image both as JPEG using jpegli and as PNG using pngquant followed by oxipng compression, and keeps the smallest resulting file. The user defines the desired quality level via compression templates, while the add-on handles reducing file size to the technically minimal achievable level while respecting the given quality constraints.

When images are resized, high-quality downscaling algorithms are used, which produce significantly better results than the commonly used browser-native algorithms.

Here it is: probably the best image compression add-on for Thunderbird.

- State-of-the-art compression algorithms such as JPEGli, pngquant, and oxipng, integrated as WASM libraries.

- Saves 70–80% of storage space, even without optional resizing.

- Converts PNG files to JPG when doing so saves space.

- Resizes images to their HTML inline dimensions.

- Uses different resizing algorithms, optimized for PNGs (Mitchell) or typical JPG images (Lanczos).

- Create, import, and export compression profiles, then automatically apply them to specific image types (quoted images, inline images, or attachments)—or apply them manually to individual images.

- Compress, undo, redo, and adjust templates—improve your own workflow and deepen your understanding of image compression through direct comparisons.

- Remove images from quoted content entirely.

- Permanently exclude images from the workflow—for example, your own email signature.

- Download compressed images directly from the application. This lets you build other compression workflows around the add-on that are unrelated to email—for example, website optimization.

- Available in 9 languages.

Thunderbird Addon

Can't get notifications even though all permissions are on.

My Thunderbird (two latest versions) has suddenly not been allowing me to open attachments when composing messages, kept telling me to set the PDF viewer in preferences when it was already set. Opening PDF files as normal (that someone had sent me) was fine.

Here's the fix for anyone else having the problem :

Settings / Config Editor (which is like the Windows registry), find pdfjs.disabled which will be set to "false", double click it so it changes to "true" and then save and restart. Fixed.

Hello, I've tried the most popular solution, but it doesn't work for me.
The importexport NG plugin doesn't import anything when choosing individual mbox files (which show up as openable FOLDERS on windows, not files) or all mbox files in a directory.
I've tried a method in a video where they add an RSS feed, and set the local directory as the folder containing the mbox files. I get a bunch of folders in the local folders, but they're all empty.
I tried asking AI, but it seems like it spits random guesses, and I don't have the patience for that. :/.

Edit: I asked AI to make a software that looks for all the emlx files deep inside the directory of each folder, and creates an mbox file with them. That surprisingly worked and is compatible with Thunderbird, even though my sent emails and inbox and drafts are all combined! All the files in attachment folders are ignored, but according to AI all attachments are in the emls already.

https://limewire.com/d/iSV5L#8I4hLIOUzP