The recipient (Gmail in this case), receives a message similar to the below. Click ‘Read the message’ and they will be taken to a website. NOTE: THIS ONLY OCCURS FOR EMAILS OUTSIDE OF MICROSOFT 365. OUTLOOK USERS ALREADY AUTHENTICATED TO O365 WILL AUTOMATICALLY BE ABLE TO READ THE MESSAGE.
The website will then ask them to sign in to view the encrypted message. They can sign in with an existing identity based on their email system or receive a one time passcode via email.
The message is then displayed in the portal and the user can reply from there.