There is a new option that has been made available for our Office 365 customers that allows you to take advantage of integrating the OneDrive for Business attachment experience directly from your OWA and Outlook 2016 clients. The main point of this feature is to allow you to insert a link and properly permission a document that is stored in a OneDrive account. This will prevent you from having to send a traditional attachment to a set of users only to go through the painful tasks of merging all of the comments and changes. Instead, you can send the document via a OneDrive link that can all be edited from the same source location.
If you have an Office 365 mailbox and a OneDrive for Business account, you are all set, this functionality will just work.
Read more at source: http://blogs.technet.com/b/exchange/archive/2015/11/04/modern-attachments-for-exchange-2016-hybrid-customers.aspx