Hopefully Hashfast's customers won't want to scam each other, so the fears of that may be overblown.
It's far from overblown IMHO. Do you know how easy is to compose an email with a GIF inside with link to a server which will log that email's IP address at the very moment you open that email to read it?
I said hopefully. And if you haven't turned off autoloading images in your e-mail yet (I did years ago), then I guess now is the time to do it!
Making lemonade out of lemons, the upside is in organizing the batch one customers. You think Hashfast is feeling pressure now? What if they got a letter about the MPP signed by a very large number of their customers?