Add support for sub-tasks in Thunderbird

[Ponda]

Thunderbird can act not only as a mail client, but also calendar, address book, tasks app and more, which gives new productivity opportunities – for example, you can very easily convert an e-mail into a task or event. One of the things Thunderbird currently lacks, however, is support for sub-tasks/hierarchical to-do. Let me show you this amazing feature on an example (using Nextcloud Tasks):

On Bugzilla, this feature was requested 21 years ago: https://bugzilla.mozilla.org/show_bug.cgi?id=194863

There are no good desktop apps supporting caldav and sub-tasks that I'm aware of, and the only such app for Android is Tasks.org. In addition, it seems Thunderbird already supports necessary attribute: https://github.com/Betterbird/thunderbird-patches/issues/79#issuecomment-1465267112

[Padacore]

I would also greatly appreciate this feature.

[mikebass]

This feature is really needed in combination with NextCloud tasks.  🙏

[futuref]

So much work to do, but only Nextcloud and my Android ecosystem knows about my sub tasks 😞

Thunderbird is dying slowly...

[PeterSM]

Another Request for Sub-tasks. (With sync to Nextcloud, of course!)

[trojan_eyebrows]

@Jon did the team get back to you on the progress by any chance? 

---

@Jon wrote on 05-05-2025 05:53 AM :

thanks for the tag! Let me check with the team to see if there are any updates.

---

[wsm]

At present there is no change in status.  The work on calendar planned for last year and this year was largely delayed due to focus on other Thunderbird feature work, but calendar work is resuming shortly.  Unfortuantely subtasks is not yet on any planned work for this year or next because there is much calendar work to be done to improve and repair before we get to subtasks.

[trojan_eyebrows]

Thanks for the update, @wsm! Even though it's further away than I'd hoped, I think we all appreciate not being left in the dark. 💙

If someone were to check in on the 2027 timeline, when would be a good time to do so? Perhaps late 2026, say, October?

[Otoro]

Thanks for the update @wsm 
Although it's not very encouraging 😞
If it's neither planned this or next year... then it feels like it's never gonna happen 😞 (considering this has been requested again and again over the years)

Where we can check the planned roadmap? 
Maybe there's something that could be pushed back to give some space for the much needed subtasks? 🙂

[wsm]

I am expecting the next roadmap to be published in a month or two.

Watch https://thunderbird.topicbox.com/groups/planning/ and/or https://blog.thunderbird.net/