Hello Mail app users and contributors 
After a few months, I plan to release a new version of Mail: v0.12. This version comes with a completely rewritten front-end as we had to find a replacement for the outdated Backbone Marionette framework. The new front-end is written in Vue and has become easier to maintain and fix bugs. You can find the release PR with all linked alpha, beta and RC builds on Github: https://github.com/nextcloud/mail/pull/1594
Please let me/us know if you find any unexpected behavior, bugs or regressions 
Cheers
Christoph