Post Office
Use this module if you want to make it possible for members of this class to exchange private messages.
Think of the Post Office as an email system open only to members of
this classroom. You can send a private message (with optional
file attachments) to one or more students, a student can send you a
private message, and students can address messages to each other.
Compared to ordinary email, the Post Office is a better choice for
an online class. It's organized, free of spam, and the sender of
a message can check if and when a message has been opened or deleted.