Me too, it classifies mailinator as risky. I use it everywhere.

I use the name of the company that offers the 'free' wi-fi - eg nothanks@mcdonalds.com or chairman@walmart.com etc. That way they get the bounce back on their own mail servers and they also rarely refuse to accept it as a valid address for some reason :)

(note I'm just using mcD & walmart as place-holder company names, have no idea if they operate their public wi-fi that way)