Thyth September 2017
Viewing, accepting, and declining invitations were added to the browser API rather than doing it via t-mail (see message #3 in this thread, specifically the userinvites, useraccept, userdecline methods). That's different from the way the game did it originally, but there's no reason it has to work the exact same way as before. There is no in-game UI to do it the new way, but, like I said above: I'm not doing any new development for TribesNext.
rJay September 2017
There is a section in the FAQ about patch 3 coming soon... I'd maybe update that. ::)
Thyth October 2017
This is a reminder to update any of your software to use the new "tribesnext.thyth.com" API hostname. If you're using the old tournamentNetClient, be sure to replace it with touernamentNetClient2. If you're using pre-RC3 code from GitHub, make sure you've pulled latest from t2-scripts/master as of September 25th. Sites using the API will need to update themselves too.
I will be making the changes to systems on my end soon without further advanced notice. If you neglect to update and your stuff breaks: you have been warned.