You have very little to lose by giving the guy a free copy and hundreds of dollars to gain. Avault is a very well known site. I doubt someone would go to the trouble to impersonate someone from there to scam you out of a copy of your halloween puzzle game.
I would find an alternative email address on avault, email them a copy of the letter, a link tot he game, and let them know about the email bounce.
I would find an alternative email address on avault, email them a copy of the letter, a link tot he game, and let them know about the email bounce.