I really hope @Tutanota gets its Android client into F-Droid (so far, I couldn't even find the source code for this client, only for the old cordova based one). If that's the case, I'll get a premium account to use it as secondary mailbox (and to support them).
@Tutanota @fdroidorg Happy to hear that. Given that you are going to release it under a copyleft license, have you considered developing them in the open?