Moodle offers a couple ways to communicate with students: a News Forum, Quickmail, and a Feedback block. Both will be covered below with recommendations for using both.
News Forum
This is a special forum which only allows the teacher in a course to post. the purpose of this forum is to provide class announcements. This forum will send messages to all students in a course. If the teacher desires to send messages to a subset of students another method is necessary.
Quickmail
This blocks allows the instructor to email students from within the Moodle course. This tool makes it easy to select and send a message to a single student, a small group of students, or the entire class. The Quickmail block supports attachments and email signatures. Please read through the Quickmail book to learn more about this tool. Note: Quickmail does require the user to login into their Moodle account.
Feedback
Feedback may be given to students through many of the tools in Moodle including (but not limited to) assignments, quizzes, and forums.