Betterbird Blog

Thunderbird still hasn't implemented proper support for internationalized domain names (IDNs) as these two bugs show: Bug 235312 from 2004, Bug 923043 from 2013.

In brief, sending messages to mail addresses at internationalized domains may fail, depending on whether the final server supports so-called SMTPUTF8 (RFC 6531). If it doesn't, it likely also doesn't support UTF-8 headers (RFC 6532), and delivery will fail due to raw UTF-8 in addressing headers. This especially applies to domains hosted at IONOS.

Mail clients like Microsoft Outlook and FairEmail handle the situation somewhat better, since they unconditionally force internationalized addressing headers to ASCII-Compatible Encoding (ACE), which uses Punycode as encoding.

Betterbird has now introduced the preference mail.strictly_ace (similar to mail.strictly_mime which avoids 8bit characters in mail bodies). With this preference set, Betterbird will behave like the two mentioned mail clients and force addressing headers to ACE.

Further reading:

• IDNs
• Punycode

We've shipped Betterbird 140.10.0esr-bb21 today. Please refer to the Release Notes for full details.

As the new ESR version 153 is already on the horizon being scheduled for the 21st of July 2026, development of the current ESR 140 has somewhat slowed down. The Thunderbird folks are not shipping anything in their 140.10.0 apart from security fixes in the Mozilla platform and more complete localisations.

We're shipping Betterbird for the first time in Portuguese from Portugal. This was made possible be the tireless effort or volunteer Hugo from North-Portugal. Portuguese is tricky, they have a polite verb forms, like German, French, Spanish and many other languages, and they had a orthography reform in 1990, which wasn't widely accepted, so people still use the old spelling. Thunderbird opted for the polite form and adherence to the reform, so we needed to adopt the same, much to the discontent of our translator who argued that the familiar verb forms are more adequate in today's Portugal. He also had to fix the Thunderbird localisation for Portuguese, so Betterbird (and Thunderbird) can now ship a proper localisation without "English patches" here and there. Thank you, Hugo!

By popular demand, we've changed the icon for CardDAV address books to make them more distinguishable:

Lastly, we fixed a long-standing issue with permanently decrypted PGP messages. After Thunderbird removed this feature in version 78, we implemented it in Betterbird 91, and Thunderbird followed in version 102. However, when decrypting a signed and encrypted message, the signature wasn't shown as valid any more. This has now finally been fixed:

Note that from version 115, signed and encrypted messages use a "combined" MIME layer, so when decrypting the signature is lost regardless. Therefor the fix only applies to messages created before version 115 or those which are now created forcing separate MIME layers with preference mail.openpgp.separate_mime_layers.

Thunderbird has always been underperforming when measured against its own roadmaps. Now it looks like the roadmaps have been replaced by a list of what the project is working on anyway.

Let's compare the past and current roadmaps. We're focusing on the major items which have accompanied us over the last five years, of which at time of writing (April 2026) none are complete and only one, Exchange support, has a realistic chance of being completed.

Items marked with an asterisk for 2026 (Fluent, Exhange) may be complete for the summer release of Thunderbird 153, the global database will not be shipping in this release.

Important items, like replacing the buggy 26-year-old MIME library of finally providing a decent and contemporary mail editor, are not even on the roadmap.

It's no surprise that things are not progressing with the Thunderbird desktop development, since despite close to 60 staff (of whom 15 are managers, CEO, COO or directors), the project has "diversified" into Thunderbird for Android (rebadged K-9 app), Thunderbird for iOS and so-called "Services" where the project actually supplies mail accounts. A developer recently wrote that the desktop team was small; going by the mentioned page and not counting director/manager and release engineer, there are only 12 people.