If a user sends an email to multiple recipients including Office 365 users (internal or external) as well as non-Office 365 users that don't support TLS transport and wants to protect that email with OME, it has to be encrypted. This would lead to the situation where all recipients would have to go through the portal process to retrieve the message including the Office 365 users.

This would be a reason that TLS encryption for Office 365 users to reasonably protect emails is not adequate and OME is inconvenient for Office 365 users. This is the reason for my inquiry about making message decryption transparent to the Office 365 users within Outlook 2016.

I understand that the login to the portal is to a different system than the login for email, but it seems to me that Outlook could be programmed to sense the receipt of an OME message and transparently to the user make a connection to the encryption server portal using the credentials used to log into the email server and display the message within Outlook. This would be the same login information that a user would use at the encryption portal anyway. I understand that Non-Office 365 users and Office 365 users using a different email client would still need to go through the portal.