Hardly. They get your password on login, and decrypt your mail. They don't (theoretically) even need a code change, just root/kernel level access/tracing to dump the password.

Unless of course you were using PGP - but then you would be about as well off with Gmail?

I mean, they provide a great service, and the stack is open - but I would hesitate to call it "secure" (that goes for ProtonMail too BTW).

https://0xacab.org/liberate/trees