Valid for Moodle 2.8. Updated on 2/1/2016.
Email in Amherst's Moodle is handled through the participants list. The list has been highly modified by Amherst and these instructions will not work on other Moodle installations.
Access the participants by going to the Navigation block → My courses → Course Name → Participants. This will bring up the course roster.
There are four ways to send email from the roster.
Emailing an Individual
To send email to a single individual, simply click on their email address.
Emailing a group of individuals
Click the checkbox beneath the name of every person to receive the email. Then above the list of participants, pull down the Send an email option for the With selected users... prompt. If you aren't using groups, sending mail may be your only option.
Emailing every class member with a particular role(s)
Click on the Email By Role line near the top of the page. Then click on the roles that should receive the email. Finally click on the Submit button.
At Amherst we have multiple, different student roles (student-AC, student-5C, etc). All students includes everyone in any of these roles.
Emailing the entire class
There are two ways of emailing everyone associated with the course. First, you could click on the Email this course button. Alternatively, you could click on the Select all link and then send an email to the selected users. The later approach is most useful if you want to email to most, but not every person. You start by selecting all and then uncheck the people who shouldn't get the email. This is useful since the course roster will probably include some non-students such as the department academic coordinator.
One thing to remember is that Select all only works with the individuals displayed on the screen. If for any reason the page doesn't show everyone in the course, the email will not go to those who are missing from the page. If the course is so large that the participant list has multiple pages, you first have to click on a Show all link that will appear at the top of the page.
Writing the email
No matter how you start the process, the creation of the email using the same form. You can add additional recipients to the To: field if you want to include someone not in the class. Use a comma to separate the addresses.