For informal comments, the message system built in to Moodle is a quick alternative to email. You can send someone a message that they can reply to immediately (if they happen to be online). If they don’t respond within about 30 minutes, a copy of your message will be sent to the email address that is listed in their participant profile. (This default setting can be changed to a shorter or longer time period).
Step 1: Go to Participants in the upper left corner on the main page.
Step 2: Select the participant that you want to send a message to (by clicking on their name). Click on the Send message button at the bottom of the pop-up window with the participant profile.
Step 3: After you’ve sent your message, the recipient will see a popup window with the number 1 next to your name. Here’s a screenshot that indicates that I just received a message from Bob Cole: