I can't send photos from Mac Photos with Outlook by clicking the photo icon in the email application or as an attachment.  When I try to send from the Photos program, I get many choices.  Outlook shows up in the menu when I click for more options, the box is checked, but it is not highlighted and I can't actually use it.  This may be a good sign since it wasn't there as an option at all a month or so ago.  Hopefully they are fixing this problem.  There is a message about downloading a third party extension, but I can't find anything about that on the internet or in any of the help menus.