@Michelle1661 On the message stream page with the guest, look on the left hand side of the screen, scroll down. You will see "Email" and it has a coded email address Airbnb assigns to the guest. Click on this and your own email account will come up, that coded email address will already be filled in, in the address field, and then you can send the guest an email with attachments, or info in the body of the message. The guest will see this in their regular email account Inbox (or could end up in their Spam box, so make sure to tell them to check there if they don't see it in Inbox, to check their Spam box).
You can also just right click Copy on that coded email address and paste it into the address bar in your normal email account.
I have had problems with guests getting the email, but with the attachments missing. In that case, I ask for their personal email address and send it to them that way.