As widely announced on Thunderbird forums and mailing lists, Thunderbird is diversifying. First they bought the K-9 Android e-mail client and rebadged it as Thunderbird for Android. Next, they are developing an iOS mail application from scratch. The last undertaking is to offer so-called Pro Services, called "TB Pro": www.tb.pro. See the 2025 announcement here.
The mail hosting part of those services is called Thundermail. Currently, it's not yet available, but one can join a waiting list. Expect to pay 12 x USD 6 = USD 72 anually. Not a small price, given that for less money you can resister your own domain and pay a hosting service, or have your mail hosted at our advertising partner ForwardEmail. Of course, there are also long-standing e-mail services, like Fastmail, Posteo or Proton Mail, each backed up be years or decades of experience.
All that said, the Thunderbird folks are rolling out the integration of their Thundermail service in Thunderbird 153, currently in beta, see screenshot above. Technically, Thundermail is integrated as system add-on, which ships inside the application, packaged into omni.ja at chrome/messenger/builtin-addons/thundermail. It's enabled in the new Account Hub via preference mail.accounthub.thundermail.enabled.
The Thunderbird folks are shipping their version 153.0 beta 2 with Thundermail enabled. We're currently disabling Thundermail via the mentioned preference for various reasons:
- It doesn't yet appear to be available.
- We're not convinced that this is the best possible mail hosting offer.
- Our project does not aim to increase Thunderbird income, but to improve user experience.
Most of the source code of Thundermail is only published in minified/obfuscated form. We did a quick AI analysis of what is publicly visible, and here's the summary of the US services involved in the setup:
| Company | Headquarters | What's Stored |
|---|---|---|
| AWS | Seattle, WA | Mail data, attachments, secrets, config |
| Neon | San Francisco, CA | Database (mail metadata, config) |
| Backblaze | San Mateo, CA | Encrypted file uploads (Send) |
| Cloudflare | San Francisco, CA | DNS, traffic routing, TLS termination |
| Sentry | San Francisco, CA | Error telemetry from add-on |
Any Betterbird user wishing to try or use Thundermail can easily set the preference to true.
Update 25th June 2026: We've just been made aware that apart from showing "Sign in with Thundermail" during account creation, Thundermail is also forced onto the application menu:
The DOM ID of this element is tbpro-menu-id-root; it is added here.
The add-on code is extracted from this repository and pushed into the Thunderbird tree. Here it is:
This code is not indexed in Searchfox.
Packaging software some or most users don't want into the application via some system add-on sounds like something Mozilla has done before? Well, check this Lunduke video.