Office 365 S/MIME

[discoveranother]

Hello

 

Have a couple of users who are using the online Office 365 version for emails. Encryption is setup for them and has been working fine, but a couple of users are now getting the following message:-

 

You can't sign or encrypt this message until the S/MIME extension has been installed. Please contact your IT administrator for help installing the extension.

 

How do I set this up please.

 

Thank you for any responses.