A RESTful API for a simple contact form service. It is to receive contact details (name, email and message) and persist the data. Confirmation of a successful submission to be sent to the email supplied. There should also be an endpoint to view all messages and individual messages. No authentication is required, nor end client to consume endpoints.
Things to consider:
Although this is only a very simple task, please approach it as you would if it were a small part of a medium-large website. You should make your code easy to test and maintain.