Do you drive 66 MPH in a 65 MPH zone? This is hardly breaking the law. This would have been perfectly legal in CAN-SPAM if they added three things: an unsubscribe link, a physical mailing address, and mentioned it was an ad. It probably would have been even more effective.
If you want to stop spam, don't rely on bureaucratic processes to resolve it through legislation. Build a spam filter, or do some simple pattern recognition so you know that the same message sent 100 times isn't a legitimate inquiry to a posting.
No, unsolicited email is never legal, CAN-SPAM only allows you to send email to people you have a prior business relationship with e.g. they signed up for your service/mailing list. Someone who posted a property to Craigslist hardly fits the profile.
Nobody here knows how much of Airbnb's growth is driven by Craigslist, it's purely speculative. Until Airbnb confirms, you'll never know but you'd have to be naive to believe that you can build a company up to $1 billion by firing off a bunch of emails. Nobody here has even suggested the possibility that "Airbnb became a billion dollar company" by suggesting how many Craigslist rentals are posted each day, along with a standardized conversion rate.
I'm surprised to see how negative the comments are on this. This is like Yelp paying people to write reviews. Shady? Sure. Illegal? The only part of the CAN-SPAM Act Airbnb broke was (1) not including a physical mailing address, (2) not mentioning it was an ad, and (3) not including an unsubscrive link. Otherwise, CAN-SPAM is laughable at best. It's hardly enforced. Don't expect Craigslist to come at Airbnb with a lawsuit, it'd probably not hold up in court.
I see this instead as one of Airbnb's many tactics to try and reach out to users. If you look at this logically, they've been covered by the press a lot. The amount of growth they might (or might not) have reached doing this would hail in comparison to how much they obtained by press and simple product and customer development.
Saying "the only part" of the law airbnb broke and then listing 1,2,3 violations is laughable.
Also I quite enjoy the irony that an account name of throwaway is defending the practice of using throwaway gmail accounts to spam people. Warms the cockles.
If you want to stop spam, don't rely on bureaucratic processes to resolve it through legislation. Build a spam filter, or do some simple pattern recognition so you know that the same message sent 100 times isn't a legitimate inquiry to a posting.