A little while ago, it was announced that Thunderbird was, sort of, coming to Android ( see https://news.ycombinator.com/item?id=31725103 ). The UserLAnd Technologies team thought, why don't we bring it to Android for real? So we have and it is now on the Play Store ( see https://play.google.com/store/apps/details?id=tech.ula.birdb... ).
This is the first release of the actual desktop version of Thunderbird. It has some bumps currently, for example there is a awkward pause before Thunderbird is displayed, but we will improve BirdBox over time and we don't see any issues that cannot be solved in future releases.
We are charging for this app to help fund our open source work, but you can run Thunderbird in our free app, UserLAnd, if desired. BirdBox will allow us to create a more convenient and tailored experience for Thunderbird users. Any improvements developed while working on BirdBox will find their way back into UserLAnd.