I suggest that Airbnb remove the automatic message that is sent when a co-hosting proposal is sent. When a co-host, or host, sends a proposal, a message stating: "proposal sent!" automatically sends. I am not a fan of automatic messages, especially when it can be assumed that the two individuals are already in communication. Additionally, a notification email is sent to both parties regarding the proposal.
For example: after a few days of meeting and discussing a co-hosting opportunity, I sent a proposal to the host today. As we were in the middle of chatting via the Airbnb messaging platform, an automatic messages was relayed ("proposal sent!") each time I sent the original proposal, and then again when I made an edit.