Invite users to secure their email communication

[4jNsY6fCVqZv]

https://github.com/elementary/installer/wiki/Encryption

Just wondering if the other way around makes sense: Similar to a WLAN network, my idea would be to set "secure = end to end encrypted" as default and mark all other transport methods as insecure.
Together with an explanation, this would perhaps make people more conscious about how normal email communication is close to sending postcards.
As soon as Mail supports encryption of e-mails by default #343 or (hardware-based) two-factor authentication for accounts #345 & elementary/switchboard-plug-onlineaccounts#89, users could also be invited visually in the user interface to make their e-mail communication more secure in the future and to provide inspiration for how this can be achieved.