Support for decrypting GPG- or S/Mime-encrypted mails?

[e-alfred]

Hello,

would it be possible to allow decryption of GPG or S/Mime-encrypted mails? This would make transmission over different mail servers more secure because only the Nextcloud server would have to be trustworthy. None of the other parties involved in the transmission would be able to see the content of the mail after all.

Aside from tools like Enigmail/GPG4Win/Kleopatra, a gateway like Zeyple (https://infertux.com/labs/zeyple/) could do all the encryption on the sender side, so people wouldn't have to set up anything locally at all.