April 2017 updates
Set permissions on OneDrive email attachments
If you send a link to an attachment stored on OneDrive, you now have more control over who can read or who can edit your attachment. You can allow anyone in your organization to read or edit the attachment or limit access just to the recipient. If you try to send an attachment stored on a SharePoint online site and your recipient won't have access to the attachment due to permissions restrictions, Outlook will warn you and suggest you attach a copy of the attachment instead. For more information, see Attach a file to an email in Outlook for Windows.