I'm wondering if it's possible to create a message board type of system within a PHP/MySQL database-driven site?  It's just for customers who are logged in to be able to send and receive private messages.

Well, I'm brainstorming contact  methods for my clients using my website, if it were database-driven (it's not at the moment). 

Instead of my clients emailing me questions or concerns, they could just  login into the database (website), go to their client page and submit a comment all from their client page.  The response to their inquiry would be visible on their account page and only if they were logged in.  Am I making sense?

Part of me thinks this function would be beneficial for them and part of me thinks it could be a waste of time (putting  it all together once I even begin to figure out how to in the first place) =/