This blog post made me curious about Chatmail.  I like the Delta Chat project since years but Chatmail is different. Tempting to try this soon 🙂

https://blog.feld.me/posts/2025/03/deltachat-is-actually-good-though/

And not related to Chatmail but also tempting to test this DeltaTouch app for UbuntuTouch mobile devices https://codeberg.org/lk108/deltatouch