Explanation/Reference:
Explanation:
As an Office 365 global administrator, you can create mail flow rules, also known as transport rules, to help protect email messages you send and receive. You can set up rules to encrypt any outgoing email messages and remove encryption from encrypted messages coming from inside your organization or from replies to encrypted messages sent from your organization.
To view encrypted messages, recipients can either get a one-time password, sign in with a Microsoft account, or sign in with a work or school account associated with Office 365. Recipients can also send encrypted replies. They don't need an Office 365 subscription to view encrypted messages or send encrypted replies.
References:
https://technet.microsoft.com/en-us/library/dn569289.aspx
https://technet.microsoft.com/en-us/library/dn569287.aspx