The Close.io integration is a native one way integration. You can choose to create a new lead in Close.io based on events happening in Prospect.io.
Here is the configuration screen:
You can choose when you want to create a new lead. For example, you can ask Prospect.io to create new leads when a prospect replies to your email.
If the lead is already present in your Close.io account we don't do anything.
You can choose to copy all emails in your Close.io account. The emails will be visible in the lead page.