@ploum @LenticularCloud @aaribaud @protonmail IzzyOnDroid is not F-Droid. When you add a third party repository to F-Droid, you get apps directly from that repository without *any* checks from F-Droid.
Izzy is pretty trustworthy, his repo grabs apps straight from GitHub/GitLab/etc. of the developers, but there are no checks if the .apk file matches the source code in question and apps may contain proprietary code.
But yeah, Proton Mail is not in F-Droid. It is in IzzyOnDroid. Not the same.