Due to the occasional unreliability of the Airbnb system, @Gina32 , I take a multi-pronged approach to communicating with guests.
Like @Michelle-and-Mark2 , I contact upcoming guests about 2-3 days prior to their arrival. I confirm their arrangements and ask for their personal e-mail address and cell phone number (some guests use a home or business number for their profile). I also provide my same information.
When I send their check-in information, it goes to BOTH the Airbnb message system AND their personal e-mail address. This way if there are problems with Airbnb (and there have been), most guests still have access to their personal e-mail and still receive the information.
As a final back-up, I can send a text message to the guests (or they have alternate ways to contact me).
This has proven valuable in various situations.