With Enhanced Protection, you can privately reply to any email received through Mail Relay. From your email client, Simply reply to any received email and Mail Relay takes care of the relaying it back to the original sender.
While relaying outbound mail, Mail Relay provides you with Metadata Leak protection. This ensures your personal information is never leaked to your recipients nor to their email providers.
If you have encryption enabled, you can encrypt the replies and Mail Relay will be able to decrypt them before relaying them to their destination. Depending on your email client, you might need to “accept” (AKA “trust” or “verify”) the signature of the received email before you can encrypt your email reply. This applies to both PGP and S/MIME.