The problem happens for users who encrypt the email using the settings under the email File dialog (File > Encrypt), Microsoft further explained. To prevent the issue, there are two possible ...

Microsoft has confirmed a known issue that prevents recipients from opening encrypted emails in classic Outlook.

Outlook supports standard emojis. Compatibility depends on the version and device used. Windows has a built-in emoji keyboard ...

Classic Outlook tells you to open the email to "read its contents and verify your credentials," but that doesn't work.