Level 32
Proton has announced that ProtonMail apps across all platforms are now open source and have passed independent security audits. The firm was able to make the announcement after its Android app was open sourced today. Proton has also released SEC Consult’s full audit report of the Android app which states that the app has no outstanding vulnerabilities.

In its statement, the firm explained why the open sourcing of all its apps is important:
“One of our guiding principles is transparency. You deserve to know who we are, how our products can and cannot protect you, and how we keep your data private. We believe this level of transparency is the only way to earn the trust of our community.

To that end, open source has long been a priority at Proton. Our web app has been open source since 2015, our iOS app is open source, our desktop Bridge app is open source, and all ProtonVPN apps are open source. … Today we add the ProtonMail Android app to this list.”


Level 26
In my opinion it would be better if they would start support standard protocols like IMAP and SMTP instead of doing own.
A big problem nowadays.

And no, their own encryption doesn't make a difference to normal IMAP/ SMTP as that only works if opposite use that same service which is with email mostly not the case.