Mailbox (Inbox,Sentbox)

Question

Hi,
In my Employer site, I want the employer to send a message to an existing employee whose details are already in the database (so, there will be a user id for the employee).
The employee should receive this message when he LOGS  IN to the site in HIS INBOX and also the employer should be able to view the sent messages in his SENT BOX.
Is there a way to do this?

Thanks,