Outlook add-in : Inconsistent @odata.type for .msg files

问题

Since shared mailbox is not supported via EWS, which we used for downloading .msg (ItemAttachments) and all other attachments were downloaded over REST

We updated the outlook add-in to filter any 'ItemAttachments' and display them as un-supported for shared mailbox, which works fine. But while testing, I found that some .msg files were being downloaded via REST which was surprising and a concern.

Finally got to re-create and found that:

1. When a mail is dragged and dropped within outlook into a compose window, it attaches the attachment as: @odata.type: #Microsoft.OutlookServices.ItemAttachment

2. When a .msg file is dragged and dropped from desktop into a compose window, it attaches the attachment as: @odata.type: #Microsoft.OutlookServices.FileAttachment

Just wondering why is this? This scenario is on Outlook web and Outlook desktop windows on Outlook mac the attachments are attached as a .eml file.

It just makes it confusing to tell the user that some .msg files are supported and some are not.

来源：https://stackoverflow.com/questions/62550158/outlook-add-in-inconsistent-odata-type-for-msg-files