You can enable private messages, a feature through which people can send each other messages that aren't visible to everyone else in the way that discussions are. A person receives and reads a private message through the Private Messages tab on their profile. Using the admin console, you can enable and configure the private messaging feature.
Admin Console: System > Settings > Private Messages
Private Message Settings
In the admin console, you can enable the feature. You can also enable email notifications for messages, so that a recipient receives an email when they've received a private message (you can edit the template for the Private Message Notification email -- see Managing Email Templates for more information).
You can limit the number of messages a user can send.
People using the feature have access to an email-style UI where they can compose, view, and organize messages.
