Encrypt messages by using S/MIME in Outlook on the web
A digitally encrypted message can only be opened by recipients who have the correct key. A digital signature assures recipients that the message hasn’t been tampered with. Notes: Outlook on the web requires a Windows desktop device to support S/MIME.
Applies To:
Outlook.com, Outlook on the web for Exchange Server 2016, Outlook on the web for Exchange Server 2019