New IRM Option to Control Decryption of Attachments of Encrypted Messages

Microsoft has released a new setting in the tenant Information Rights Management (IRM) configuration to control if attachments of messages encrypted with the Encrypt Only feature (in OWA and Outlook) are decrypted when downloaded. In fact, two settings are available. One for people with Azure AD accounts, and one for those without.
https://office365foritpros.com/2018/08/24/irm-encrypt-only-attachment/