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Thunderbird’s Future Home


The investigations on Thunderbird’s future home have concluded. The Mozilla Foundation has agreed to serve as the legal and fiscal home for the Thunderbird project, but Thunderbird will migrate off Mozilla Corporation infrastructure, separating the operational aspects of the project.


In late 2015 Mitchell Baker started a discussion on the future of Thunderbird, and later blogged about the outcome of that, including this quote:

I’ve seen some characterize this as Mozilla “dropping” Thunderbird. This is not accurate. We are going to disentangle the technical infrastructure. We are going to assist the Thunderbird community. This includes working with organizations that want to invest in Thunderbird, several of which have stepped forward already. Mozilla Foundation will serve as a fiscal sponsor for Thunderbird donations during this time.

To investigate potential new homes for Thunderbird, Mozilla commissioned a report from Simon Phipps, former president of the OSI.

The Last Year’s Investigations

The Phipps report saw three viable choices for the Thunderbird Project’s future home: the Software Freedom Conservancy (SFC), The Document Foundation (TDF) and a new deal at the Mozilla Foundation. An independent “Thunderbird Foundation” alternative was not recommended as a first step but the report said it “may become appropriate in the future for Thunderbird to separate from its new host and become a full independent entity”.

Since then the Thunderbird Council, the governing body for the Thunderbird project, has worked to determine the most appropriate long term financial and organizational home, using the Phipps report as a starting point. Over the past year, the Council has thoroughly discussed the needs of a future Thunderbird team, and focused on investigating the non-Mozilla organizations as a potential future home. Many meetings and conversations were held with organizations such as TDF and SFC to determine their suitability as potential homes, or models to build on.

In parallel, Thunderbird worked to develop a revenue stream, which would be needed regardless of an eventual home. So the Thunderbird Council arranged to collect donations from our users, with the Mozilla Foundation as fiscal sponsor. Many months of donations have developed a strong revenue stream that has given us the confidence to begin moving away from Mozilla-hosted infrastructure, and to hire a staff to support this process. Our infrastructure is moving to and we’re already running some Thunderbird-only services, like the ISPDB (used for auto configuring users’ email accounts), on our own.

Legally our existence is still under the Mozilla Foundation through their ownership of the trademark, and their control of the update path and websites that we use. This arrangement has been working well from Thunderbird’s point of view. But there are still pain points – build/release, localization, and divergent plans with respect to add-ons, to name a few. These are pain points for both Thunderbird and Firefox, and we obviously want them resolved. However, the Council feels these pain points would not be addressed by moving to TDF or SFC.

Thus, much has changed since 2015 – we were able to establish a financial home at the Mozilla Foundation, we are successfully collecting donations from our users, and the first steps of migrating infrastructure have been taken. We started questioning the usefulness of moving elsewhere, organizationally. While Mozilla wants to be laser-focused on the success of Firefox, in recent discussions it was clear that they continue to have a strong desire to see Thunderbird succeed. In many ways, there is more need for independent and secure email than ever. As long as Thunderbird doesn’t slow down the progress of Firefox, there seems to be no significant obstacles for continued co-existence.

We have come to the conclusion that a move to a non-Mozilla organization will be a major distraction to addressing technical issues and building a strong Thunderbird team. Also, while we hope to be independent from Gecko in the long term, it is in Thunderbird’s interest to remain as close to Mozilla as possible to in the hope that it gives use better access to people who can help us plan for and sort through Gecko-driven incompatibilities.

We’d like to emphasize that all organizations we were in contact with were extremely welcoming and great to work with. The decision we have made should not reflect negatively on these organizations and we would like to thank them for their support during our orientation phase.

What’s Next

The Mozilla Foundation has agreed to continue as Thunderbird’s legal, fiscal and cultural home, with the following provisos:

  1. The Thunderbird Council and the Mozilla Foundation executive team maintain a good working relationship and make decisions in a timely manner.
  2. The Thunderbird Council and the team make meaningful progress in short order on operational and technical independence from Mozilla Corporation.
  3. Either side may give the other six months notice if they wish to discontinue the Mozilla Foundation’s role as the legal and fiscal host of the Thunderbird project.

Mozilla would invoke C if A+B don’t happen. If C happened, Thunderbird would be expected to move to another organization over the course of six months.

From an operational perspective, Thunderbird needs to act independently. The Council will be managing all operations and infrastructure required to serve over 25 million users and the community surrounding it. This will require a certain amount of working capital and the ability to make strong decisions. The Mozilla Foundation will work with the Thunderbird Council to ensure that operational decisions can be made without substantial barriers.

If it becomes necessary for operational success, the Thunderbird Council will register a separate legal organization. The new organization would run certain aspects of Thunderbird’s operations, gradually increasing in capacity. Donor funds would be allocated to support the new organization. The relationship with Mozilla would be contractual, for example permission to use the trademark.

A Bright Future

The Thunderbird Council is optimistic about the future. With the organizational question settled, we can focus on the technical challenges ahead. Thunderbird will remain a Gecko-based application at least in the midterm, but many of the technologies Thunderbird relies upon in that platform will one day no longer be supported. The long term plan is to migrate our code to web technologies, but this will take time, staff, and planning. We are looking for highly skilled volunteer developers who can help us with this endeavor, to make sure the world continues to have a high-performance open-source secure email client it can rely upon.

63 responses

Philipp Kewisch wrote on

I’m going to make the first comment my own. Now that we have our financial home settled I think it would be a great time to make a donation to support our work. While the Mozilla Foundation is our financial home, it is up to us to raise the funds needed to make sure Thunderbird is a modern and secure email client for years to come.

If you would like to help us out, please head over to Your support means a lot to us! Maybe you would even consider a recurring donation, as this would help our success in the long term.

Ian Thomas wrote on

How separate are we talking? I can see the ISPDB is quite an independent service and I can see things like build infrastructure being separated too. What about the more public-facing but more shared services, such as the website (, downloads or even this blog?

You mention in the future needing to licence the trademark from Mozilla. Does this refer to “Thunderbird” or “Mozilla Thunderbird”?

Philipp Kewisch wrote on

We will prioritize services that are either simple to migrate or currently require extra maintenance by Mozilla Corporation staff. As you mentioned, build infrastructure is one of those services and pretty high up on the list. The website is already in the process of being moved to, which includes separate hosting. We will collaborate with Mozilla to ensure a good prioritization, at the time I do not know what services will continue to be hosted by Mozilla once we are done.

Regarding trademarks, Thunderbird is a registered wordmark for Mozilla, so without permission we cannot use either Mozilla Thunderbird or Thunderbird. We don’t need to go through this process at the time since the Mozilla Foundation is our home.

Ian Neal wrote on

Where do the likes of bugzilla, hg and dxr for comm-* sit on the order of migrations to

Philipp Kewisch wrote on

We haven’t given each item a priority yet, but I suspect these will be fairly low on the list.

Dimitris Glezos wrote on

Philipp, happy to help you guys with localization over at

Philipp Kewisch wrote on

Very much appreciated Dimitris! I’ve written this down, we will get back to you once we start to tackle localization.

pascal wrote on

Watch out, “happy to provide localization” to open source projects and later their team contact you and ask for big paycheck! Not nice, or be ready to pay them big money.

A wrote on

I went through the article and I now understand what will happen, but I do not understand why. Why Thunderbird can no longer be developed by Mozilla?

Ian Thomas wrote on

See the links to Mitchell Baker’s posts for detailed reasons, but it basically boils down to Mozilla having limited resources (time, money, executive attention) and not considering Thunderbird as important for their mission as Firefox and other projects are.

A big part of this split that has already been announced is that Thunderbird will no longer share a codebase with Firefox. That allows Firefox developers to make larger changes faster and means Thunderbird developers won’t have to spend time fixing problems created by changes in Firefox. It also means that the code bases will increasingly diverge.

S S wrote on

Will Mozilla continue to still support the Thunderbird addon website after switching Firefox to Webextensions for Firefox? Or does this count as separate infrastructure that the Thunderbird foundation must maintain?

Philipp Kewisch wrote on

We are in contact with the add-ons team (in fact, in my day job I am on the add-ons team). We haven’t finalized the decision on this, but I can confirm that we will be making sure add-ons continue to be available for Thunderbird in the future.

Axel wrote on

Addons will stay and I hope XUL and XPCOM will stay supported for much longer than in Firefox. Mozilla wants to kill off this important technology mainly for safety reasons, but a lot of important Addons in the mail area are based on it.

Philipp Kewisch wrote on

At the time, there are no plans to restrict what add-ons can do in Thunderbird. We will continue to support legacy add-ons for as long as possible. Given our current dependency on the Mozilla Platform and the upcoming changes in Firefox 57, it may become increasingly difficult to support XUL/XPCOM add-ons. I believe there has been some discussion on this topic on tb-planning if you are interested in further reading. In any case, we would like to work with Thunderbird add-on developers to define what add-ons could look like going forward.

Kevin Swan wrote on

I believe that Postbox was built from the Thunderbird code base. Are they involved with Mozilla or Thunderbird in anyway? Will they contribute to the continued support of Thunderbird or did they fork the codebase and maintain it separately?

Philipp Kewisch wrote on

Postbox is separate from Thunderbird, they have forked their code. We are open to discussions with other organizations if there is a benefit for our community. I do not know if they plan to upstream some of the code or support development of a future version of Thunderbird.

Seris wrote on

Do NOT use any web technologies please, stay native.

Philipp Kewisch wrote on

Thunderbird has been using web technologies or related technologies since its existence. There are certainly benefits for creating a native application, but of course also drawbacks. If you would like to get involved in the future of Thunderbird, I’d suggest to visit the tb-planning group.

Hervey Allen wrote on

I am _very_ happy to see this development, but was, also, dismayed to see you report that… “The long term plan is to migrate our code to web technologies…” – I’ve joined the tb-planning group to provide my input. A native application is mission critical for myself and many of the people I work with. I love Thunderbird, but if a native application were no longer offered I would be forced to migrate away.

Philipp Kewisch wrote on

Maybe there is a misunderstanding here what “web-technologies” actually means in this context. It does not mean that Thunderbird will merely be a website. Thunderbird will continue to be an application that you can install on your desktop, as it is now. The difference will be that instead of the Mozilla-specific technologies XUL, XBL and XPCOM being used, we are considering working towards “web-technologies”, where HTML and pure JavaScript are used. From a user perspective, the experience regarding installation and use will not change.

EDIT: Also, as the operating system does not run Javascript natively, there will always be a certain part of Thunderbird that is “native”. For example, to show native notification popups, OS integration for file association and the likes, or proxy and other network settings.

Charles wrote on

I for one was hoping for TDF as the new home, so, how I feel about this depends on whether or not Mozilla makes good on their promise regarding a substantial financial ‘parting gift’ for the Thunderbird Team from Mozilla, as was imparted to me in a private email by one of the Thunderbird Council members (once the new legal home question had been finalized).

So, Philip – any news on this? 1/10th of one percent of Mozillas annual income would be about $5 million, which should not only pay for the infrastructure migration, but also provide a large chunk towards the Thunderbid++ rewrite.

Inquiring minds want to know…

Philipp Kewisch wrote on

I’d like to avoid any speculations about financial aids until there are concrete plans, as it just causes confusion and misunderstandings. Assuming such promises had been made, I am sure Mozilla would commit to their promise. As mentioned in the post, we plan to stay with the Mozilla Foundation at this time, so a “parting gift” would not be the right sign.

The Council will be looking into different ways to increase funds in order to secure the future of Thunderbird. We welcome contributions of any size from both individuals and organizations.

If there are any developments in the future along the lines of what you suggested, I am certain we will make an announcement about it.

Michał T wrote on

FYI, 1/10th of one percent of Mozilla Foundation revenue would be around $500,000 dollars by 2015 numbers (from

David Pilsner wrote on

Thunderbird Council needs to hire a staff it can’t expect to efficiently manage a project without paid staff.

Philipp Kewisch wrote on

We have actually hired for two roles and are expanding this in the future. We are currently looking for a build engineer and soon also a community manager. There are also other roles we are interested in, but given there is a certain overhead involved in the hiring process we can’t handle them all at once.

Simon Paquet wrote on

I just donated a 100€.
Go Thunderbird!

Philipp Kewisch wrote on

Thanks Simon, you are awesome! Glad to hear you are still around, if you ever have some free time at hands we’d love to have you back!

Barry Abel wrote on

I’m glad to hear that Thunderbird has the backing to move forward, but to where? I like it as a desktop application (and I’ll like it even more when some of the new resources are put to fixing bugs), but how does the Thunderbird team see it thriving in a world where people are dividing their time between different types of devices and storing their mail in the cloud? Will there be versions of Thunderbird for iOS and/or Android, with an ability to sync them with the desktop, or will Thunderbird just be a desktop application for accessing the cloud? And if the latter, what security advantage would there be to using it?

Philipp Kewisch wrote on

The world is indeed using many more channels of communication than just email and having a more personal solution that would allow users to bundle their channels and stay on top of communication would be great! From what I have heard, there is general agreement that we need to create a platform that would allow for different kinds of communciation channels, email being one of them. As email is our core business we would put our focus on this of course.

The same goes for the mobile space. If we write our components in a way that they could also be used separately e.g. on mobile, then creating a mobile product somewhere down the line may be a viable option.

We must also keep in mind though that while we would love to, we can’t do everything at once. We’ll be starting small and scaling up. If you want to be involved with Thunderbird’s future I’d suggest to subscribe to tb-planning. Here we will be discussing the technical details.

Barry Abel wrote on

Thanks for the reply. For someone like me considering getting involved, it helps to know where people see Thunderbird heading, even if everything can’t happen at once. I took your suggestion and joined tb-planning.

Philipp Kewisch wrote on

Sounds great! If you are also interested in other opportunities to contribute please do get in touch.

Ryo wrote on

It is time for a x64 version of Thunderbird for Windows after years of daily (and no Earlybird or beta!).

Philipp Kewisch wrote on

I think the build engineer we are hiring would be a great fit for working on this. It would be nice to serve the community with 64 bit windows builds!

S S wrote on

Thank you for responding to these comments and addressing our comments and concerns. Far too often, blog posts are used to make announcements, but many valuable points are made in the comments that never get posted elsewhere or addressed. This is the type of engagement with users Mozilla needs to effectively engage with the Mozilla community and userbase.

Philipp Kewisch wrote on

The community is most important to us, this is really the reason we are doing it. We’d like to create something the community enjoys and makes our users happy. Of course we will not be able to satisfy everyone, but we are doing our best. Thanks so much for the comment!

Aurizen wrote on

Does this mean new developments will finally be coming? Thunderbird is behind and I’d LOVE to come back to the greatness.

Philipp Kewisch wrote on

Yes, indeed! The Thunderbird community is already doing a great job keeping up with Mozilla platform developments, but we want to be able to do more than that. We’d like to provide the community and users with a modern and functioning email client that helps make their lives easier. Modernizing Thunderbird is just one of the ways we can achieve that.

Aurizen wrote on

I like the sound of that! Will they be able to have rapid release my Firefox?

Philipp Kewisch wrote on

We haven’t decided to change the release schedule. While we would love to get our changes out to users quicker, more releases means more overhead. If you’d like to get updates more often, maybe you’d like to consider switching to a beta build?

Evilham wrote on

Great to read this, I had the feeling Thunderbird was totally abandoned, now I see it was in-between phases.

Please, please, please, consider CardDAV and as a core feature; this has been a main pain point for ages and none of the existing plugins solve it properly.

Keep up the good work!

Philipp Kewisch wrote on

You may be interested in the CardBook extension. We definitely want to be able to support CardDAV in future versions of Thunderbird. Thanks for your support, I’m happy we could clear this up!

eggsperde wrote on

I had hoped for ODF as well, they are doing an awesome job with LibreOffice and lack an email client. But, of course, there’s the benefit of doubt for this new entity. I love TB and appreciate that you take the time to answer comments here, Philipp. Fly, Thunderbird, fly!

Philipp Kewisch wrote on

I’m glad to do so. Thank you for supporting Thunderbird!

Tom wrote on

I’ve just stumbled on this post, I’m wondering how could someone with some web dev knowledge contribute, or is it a case that one would have to learn gtk/ C++ etc. Apologies if this a dumb question.

Philipp Kewisch wrote on

There are definitely no dumb questions, I am delighted to hear you are interested. While there is a certain amount of C++ involved in Thunderbird as a whole, the frontend is written in Javascript and XUL. We are moving towards HTML though, so don’t worry too much about XUL. You are most welcome to get in touch, we can certainly use skilled web developers!

Peas ham and brown rice wrote on

I currently use Seamonkey. Is it likely to be maintained or dropped as Mozilla and Thunderbird start their new adventures?

Philipp Kewisch wrote on

I am not aware of any plans that would suggest this announcement affects SeaMonkey in any way.

Nomen luni wrote on

I find it hard to feel enthusiastic about this development. Feels too much like the status quo. Mozilla doesn’t want to invest in Thunderbird but doesn’t quite want to let it go. Add my name to those who would have liked to see it go to the Document Foundation, and if that came with a parting gift as one poster mentioned, all the better. If Mozilla gave just 1% of a single year’s revenue it could provide a real boost to Thunderbird development.

Philipp Kewisch wrote on

The status quo is that we are heavily dependent on Mozilla Corporation infrastructure and people resources in various stages of the project, and that we were not making progress with Thunderbird other than barely keeping the project alive. This is set to change. We’d love for you to take part in these discussions on tb-planning if you are interested.

I can understand if this doesn’t feel like a lot has changed on the outside because it is still Mozilla and if you look at the very recent past not much has changed. But if you go back to when we started the discussions around the financial home, we’ve made great progress. We are able to collect donations and we were able to hire contractors that help us empower the community, looking for more roles in the future. The situation we are now in with Mozilla gives us clarity and allows the council to take an active role in pushing Thunderbird forward.

Nomen luni wrote on

Thanks for the reply, Phillip. Of course, it goes without saying that you are more informed on this issue than I am so I guess I have some hope that your confidence may be justified. All the best.

Philipp Kewisch wrote on

Glad to hear I was able to get your hopes up. I’m sure this will work out nicely, and if for some unforeseen reason it doesn’t we can always adapt!

Wayne wrote on

> Mozilla doesn’t want to invest in Thunderbird but doesn’t quite want to let it go.

To clarify some items:

a) “Mozilla doesn’t want to invest in Thunderbird” — it has been a goal as long as 2008 that Thunderbird should be self-supporting. So this goal precedes the 2015 Mitchell Baker announcement, that was primarily a statement about Mozilla Corporation resources, not a Mozilla Foundation (MoFo) announcement. And yet, MoCo still has assisted in keeping Thunderbird building, and providing its infrastructure. They have not left us to die 🙂

b) Regarding “but [Mozilla] doesn’t quite want to let it go.”, what is announced here is all about Thunderbird’s self-determination. It changes nothing about MoCo, and the direction was not initiated by MoFo. This is a direction initiated and decided by *Thunderbird Council*.

Daniel wrote on

How technically Thunderbird differs from Firefox? Why can’t you follow the Firefox innovations and switch synchronously? I mean, you can little-by-little migrate components to Servo, keep up with Firefox. The only problem is you are limited by human resources, right?

What about Rust? It’s growing and rewriting Thunderbird may attract more audience as Rust is a good fit for such projects. Personally, I’m learning Rust and could potentially contribute, but won’t, since I’m not interested in C++ and JS.

Philipp Kewisch wrote on

The details about this are mentioned on tb-planning, especially in the proposal thread for the rewrite. I know it is a long read, so tl;dr; the main argument is that a rewrite would cost less resources than a gradual migration. Some of my own thoughts are in a more recent thread.

While rust is an interesting language, the amount of experts in this matter is still fairly low. There has not been a final decision though, if you’d like to follow along I’d suggest to subscribe to tb-planning.

just4fun wrote on

As a donator I would like to see how many donations are collected.

Philipp Kewisch wrote on

Of course. I’ll see if I can get more recent numbers on this, I believe some figures have been mentioned on tb-planning.

Amir Farsi wrote on

In first time, please add more payment options(Like: Bitcoin) to this page(

Philipp Kewisch wrote on

We are indeed looking into more payment options, thanks for the note!

Rolf Gloor wrote on

Hi Philipp
Great to hear that some progress has been made.
Now further development is now back on the center focus.
Also great to hear, that you are commited to Thunderbird as a desktop client and eMail is the basic/main focus.

For years I am using TB, and using it on both Windows and Linux (= main OS) desktops. Synching data through the web.
So please keep up a good multiplatform support.

When using an eMail client, having a strong address book (AB) is essential. In order to be flexible with the sync, CardDAV (as mentioned above by Evilham) is essential.

And I know there are addons. However, for such an important and central element for functionality, I do not rely on an addon. To strong the risk of a breakage during an update. (See below comment)
=> So please, get in the new, native AB with CardDAV support.

I use TB as a PIM (Personal Information Manager). In Linux (openSUSE LEAP 42.2), after every update, the Lightning is back to english.
For a “fully” integrated Calendar App, that should not happen.

With those 2 issues solved, TB will be suited much better for wider use.

I have donated this morning, to support your effort.
If needed, I might also help on some German Translations.

Thanks for your great work.

Philipp Kewisch wrote on

Mentioning CardBook as an extension was rather meant to be a quick solution for now. The new Thunderbird will most certainly have backend support for remote addressbooks, and I don’t see why we shouldn’t provide CardDAV support in core. As for the language issue, please get in touch with support and I am sure we can solve this situation. If you are using Thunderbird from your distro, you may want to try the stock Thunderbird from, I believe this issue does not appear there.

T.J. Duchene wrote on

I’d like to comment on the future of Thunderbird, but at the same time I do not want my comments to be taken as a criticism in any way. What I am curious about is the future directions that Thunderbird could take now that Firefox appears to be on a path to depreciating XUL and the plugin architecture.

Maintaining it on your own would be a greater burden in the sense the Thunderbird team is presumably much smaller than Firefox. The change would also mean that bugfixes and so on are no longer in sync with Firefox after they switch architecture. I’m sure this has been discussed at length, but I was wondering what you would share here – with no expectations, of course.

(Personally, I could be quite content to see Thunderbird move away from XUL, perhaps toward Qt.)

There are a number of features that I would love to see officially part of Thunderbird instead of an add-on, such as better addressbook integration with Google/social media, and PGP.

Thanks for reading!

Philipp Kewisch wrote on

Feedback is always welcome, thank you! We’ll be posting more information on roadmap planning here on this blog. Maintaining XUL would indeed be a burden we couldn’t shoulder. We’re transitioning on a similar path to Firefox and at the same time looking on where we can reduce dependencies on technology that is specific to the Mozilla Platform. Integrating features from add-ons is also something we are considering. For example, check out this post re PGP:

leiqunni wrote on

How about starting paid mail service?
I think that Thunderbirld is a way to directly convert it into revenue.

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