I begin with a registered user. What he can do:
1. Create messages ( subject + body ) to send to another registered user. The list of the users on the system will be taken either from database, either from an Application variable. The message will be recorded to a database( configured by the owner of the site ) with the possibility to be send also by email
2. When login, the registered user can see the list of messages and replies send to/by him. Also, if he has unread messages he can see an advertisement.
3. The application could be seen also from a mobile device.
What should be done also:
4. The install of the application should be easy for any developer ( xcopy or some package – like Nuget or recipe)
Please see http://msprogrammer.serviciipeweb.ro/tag/simple-messaging-system/