Say you send an email to someone asking them to review some information, but you want them to use Messages to respond, not an email. You can include a link like imessage://3035551212 that they can click on to open Messages and start a conversation. You can use a phone number or an email address. You can even put the link inside documents. The recipient must be on a Mac and have the Messages app configured for this to work.
Mac Video Tutorials and Tips for Apple Users
