https://blogs.technet.microsoft.com/exchange/2014/12/15/how-to-configure-smime-in-office-365/
https://www.experts-exchange.com/articles/18714/How-to-Configure-S-MIME-in-Office-365-Explained.html
S/MIME on Office365
it's notes
“Tell me and I forget, teach me and I may remember, involve me and I learn.” ― Benjamin Franklin.