To contact all your students in a module, the most reliable way is to use the Announcements forum normally found in the top section of a Moodle course.

The Announcements forum is a passive forum in that it only allows teaching staff to post; students are not able to post to the forum. It is – as the name suggests – designed for announcements!

Anybody who is enrolled in the course (in whatever capacity) will receive any post you make as an email.
Whenever you post to the forum, you have 30 minutes to edit or delete your post before it is marked to be sent for email. Normally, within minutes of it being marked as such, the notification is emailed to course participants.

“But what if I need to send an urgent announcement?”

Sometimes you will need a message to be emailed without delay, and this is possible by selecting a particular option before you post.

Follow the steps below:

1. Add a forum post as you would normally, entering the Subject and Message.
2. Click on the Advanced link to the right of the ‘Post to forum’ button:

3. Further settings are then revealed. Scroll down and select the Send forum post notifications with no editing-time delay checkbox (1, below) before clicking Post to forum (2):

This will bypass the 30-minute editing time and will immediately mark the post as ready to be sent by email. Moodle will email the post to your course participants at the next time it performs its check (typically within minutes).