We recently noticed with some internal testing and a partner who had a client with the same issue that Upgrading to the latest outlook does not allow us to attach documents via the drag and drop feature in CRM directly from outlook. .msg files or any extension that is compatible with CRM when dragged from the latest outlook feature this does not work. 

The reason being is office 365 and their push to continue to make their software more and more cloud/browser base does not allow CRM to work the same was as the standalone versions.

The current work around is making a local copy of the communication or attachment and then drag and dropping into CRM as per before. 

If you have the option in you Outlook like below, keep it off if you need drag and drop to work as per usual.

Unfortunately this is a Microsoft issue that we cannot do anything about until we have an update from them.

Please fine the notice here. https://learn.microsoft.com/en-us/answers/questions/1291922/unable-to-drag-and-drop-outlook-attachments-to-fil

The only way will be reverting to the older version of outlook for now.