We integrated our document and email management application designed for professionals with Outlook on all platforms - Windows desktop, Mac desktop, mobile etc. Recently we are migrating our integration from AppleScript to new Office JS add-in model. This is for Outlook for Mac and eventually it will be available for Outlook for Web and Windows platforms.
If you look at the old models like AppleScript or COM add-ins or VSTO add-ins, there is a way to handle multiple email selection. Users can select multiple email message from Inbox View of Outlook and integration can handle those messages (add-ins).
But the current model - Office JS add-ins doesn't support multi-selection from Task-pane or Command interface. This is required from an end user point of view due to 2 reasons:
1. Backword compatiblity. Old integration models (AppleScript or COM or VSTO addins) support it. So new model should also support it. Otherwise end users miss the functionality.
2. Users should be able to select and handle multiple email messages. Selecting one by one email message and filing it into DMS system is not a good UX.
3. Now when user select multiple email messages in 'New Outlook' for Mac, Outlook closes the taskpane automatically and doesn't allow user to perform an action on those messages.
So there should be a way to handle multiple email messages from Taskpane or CommandBar interface.
Let me know if you need more details.