The EU law linked does not actually recommend anything specifically, just vaguely states interoperability being a goal.
Certain apps will have certain functionality. Unless you're willing to constrain the functionality it's not really possible.
Right now everyone could already use email which supports encryption. They don't, though.
Doesn't the matrix chat app allow for this? Might be useful to learn how they do it if this is of interest.
https://matrix.org/docs/guides/end-to-end-encryption-impleme...
The EU law linked does not actually recommend anything specifically, just vaguely states interoperability being a goal.
Certain apps will have certain functionality. Unless you're willing to constrain the functionality it's not really possible.
Right now everyone could already use email which supports encryption. They don't, though.