From reading the service description, this is an encrypted messaging service that happens to have email notifications.<p>I can't write messages with my preferred mail client, can't read messages with my preferred mail client and I can't access my (old) messages while offline. non-protonmail-users will receive a notification with a link that they received a message, not the actual message that they can keep for archiving purposes, offline use etc. I wonder if and how they handle searching mailboxes.<p>Neat, but not mail.<p>edit: typo. darn.