how do I set this up and use it?

I just installed your new plugin, but can't figure out how to use it. Do you have some examples, or best practices? I looked at your video, but did not find it useful.

I put your [inbox] shortcode on my contact page, but I was unable to send myself a message. I tried stu@selip.com for send to, as well as "admin" but the display insisted I had not filled in the box.

Very confused!

Stu