How does Contact User work in Classifieds plugin?

Using Classifieds on

Set up an example classified ad:

whether logged in as a subscriber to the site, or not logged in as a visitor, it gives me the option to Contact User.

I have tried several times to send a message this way. Each time I get a notification on the screen that message was sent…

but no emails have come through to the address that set up the example classified ad.