outlook for mac drag and drop

Hi clickers2510,

Regarding using drag and drop on your Mac, if the feature works as expected in other areas you may need to reach out to the file storage developer to assist. However, you can test moving from macOS Mail to a different app or location to further isolate. If needed, the steps below found in the article here can assist. Drag and drop items on Mac

"Drag and drop items on Mac

You can drag and drop items to do things like move or copy files and folders, add an image to an email, or move text around in a document. 

1. On your Mac, select an item you want to drag—such as an image or block of text. 
2. Press and hold the trackpad or mouse while you drag the item to a new location.
3. To copy the item instead of moving it, press and hold the Option key while you drag.
4. Release the trackpad or mouse to drop the item in the new location."

Additionally, the issue may be with Outlook for Mac as there's a previous post on the Microsoft website here with a similar issue: Outlook 2016 for Mac - Drag and Drop Attachment Problem

If needed the articles below will help with contacting the developers to see if there's a work around or this is a known issue.

Contact a third-party vendor

How to contact an app developer

Cheers.