Why doesn't Outlook 2016 detect that an email is encrypted?

Question

Encryption

Corporate mail, used by Exchange. An encrypted incoming letter from an external device is displayed empty in outlook 2016, there is an attached file icon (paperclip) and that's it. On both clients, all settings have been made, certificates have been installed, public keys have been exchanged, certificates can be seen in contacts. Tell me where to dig?

Answer 1

The problem turned out to be precisely in adding to the external input. security alert text messages.

Answer 2

owa or desktop outlook?
What's in the attached file?
Is there anything about encryption in the properties of the message?