If you haven't already discovered it, there's info and a link to a beta version in this thread (go to last page of thread):
I installed it and it worked (mostly) for me on 15.3, and then suddenly it stopped working and told me I had an "unlicensed copy" and that my "trial had expired". However I did have a license for it and had it entered into the License screen of the MailHub preferences. I uninstalled it and reinstalled it multiple times after that and have not been able to get the beta working again. I've asked in a couple of other threads whether anyone else ran into the same 30 day limit, but despite lots of reports of the beta working for others, no one else has replied saying they hit the same 30 day limit. I'd love to find a solution and use the beta again, it shouldn't be limited to 30 days.