What are the requirements for running S/MIME in Outlook for iOS and Android?

What are the requirements for running S/MIME?

• Active subscription to Office 365, currently running the new Microsoft sync protocol
• Current mailbox resides within O365 tenant (must be native EXO mailboxes)
• Ability to update Exchange policy to permit pfx attachments over email
• iOS: Running 11.0 and higher
• Android: Running 4.4 and higher

See also

Set up S/MIME encryption in Outlook for Windows