It's actually very easy to prove, because the same email was sent from several different accounts: you go after AirBnB directly and shoot for discovery, get the

It's actually very easy to prove, because the same email was sent from several different accounts: you go after AirBnB directly and shoot for discovery, get them under oath to answer whether they did this or not. If you have ever been questioned under oath, you know how tough it is to lie (ping me offline for details). No point in chasing the gmail accounts themselves, that would be a dead-end.