K-9 Mail is one of the most popular free open source e-mail apps for Android devices. You can follow their official account at:
Their website is at https://k9mail.app
It's available to download from @fdroidorg, Google Play and Amazon App Store.
(You can also download the app and source from the git at https://github.com/k9mail/k-9)
This is a brand new server run by the main developers of the project as a spin-off of mastodon.social It is not focused on any particular niche interest - everyone is welcome as long as you follow our code of conduct!