I'm attempting to get Office 365 S/MIME encryption working for some of our employees, accessed at outlook.office365.com. These employees have been given e-mail accounts with one of our customers as well as certificates. They're able to access mail and use encryption through Outlook, but it would be a big help to get it working in webmail, preferably Chrome.
So far, I have used this to force install the extension: https://docs.microsoft.com/en-us/office365/securitycompliance/configure-s-mime-settings-for-outlook-..., which worked. If that's all I do, and we sign back in to the account and go to the Mail settings, the S/MIME section says we need to add outlook.office365.com to the allowed domains in the extension. If we do that and restart Chrome, the S/MIME section disappears. Remove the domain and restart, and it's back. Having SmimeOutlookWebChrome.msi installed or not does not seem to make a difference.
I think I'm missing something simple, but support through the other organization has been difficult to get and I personally don't have an account with them, so I'm having to resort to digging something up and bugging someone to try it.