Last year a new feature was introduced into Exchange Online to allow you to create an Attachment where the Attachment resided on OneDrive rather then the traditional Email attachment approach you can read more about this here http://blogs.office.com/2014/10/08/introducing-new-way-share-files-outlook-web-app/ there was also an Ignite session you can watch on how this has evolved https://channel9.msdn.com/Events/Ignite/2015/BRK2196 . MAPI has always had a rich set of attachment types since Exchange's inception to deal with Rich Text Messaging eg the various attachment types you can encounter are listed in https://msdn.microsoft.com/en-us/library/office/cc815439.aspx . In EWS these attachment types where simplified some what into either Item Attachments (for Attached Store Items) or File Attachments. To cater for this new feature a new Attachment Type called a ReferenceAttachment has been introduced into EWS in Exchange Online. To see the ReferenceAttachmentT...
Pushing the Envelope in Messaging and Office 365 Development