@Steve2743 If you go to your airbnb message thread with the guest and look at their profile photo, you will see a coded email address below that that airbnb assigns to all users. The guest sees a coded email address for you as well. It is perfectly legitimate for hosts and guests to communicate through these email addresses.
This feature has always been available, you just weren't aware of it.
When a guest email comes to your email inbox, there will be the guests' first name, then in parentheses (Airbnb user) like this : Steve (Airbnb user). At least that's how it looks in my yahoo mail.
Emailing is actually really useful if you need to attach anything to send to a guest, like a map, as airbnb messaging doesn't support attachments.