Unfortunately, Outlook on Mac doesn't support plugins. Until Microsoft decides to provide this, there is nothing we can do. (As a Mac Outlook user, myself, I feel your pain!)
There are no plans for an iOS Send tracking app, but I will bring this suggestion to the product team.
Thanks, Bob. Yeah it's frustrating. I hadn't thought about the no-plugins thing. Microsoft really don't support the Mac very well in general. I moved from a Windows system to a Mac and, whilst I absoltely love the Mac and wouldn't move back, MS products aren't as feature-laden as their Windows counterparts.
Thanks for adding the iOS app as a possibility. I came to Adobe Send from YouSendIt when they jacked up their prices massively. One thing I miss (probably the only thing) was their app so that you could see the tracking info easily anywhere.