If you want to send out a server-wide email or announcement, cPanel has a feature to email everyone who has a valid contact email address set up in their cPanel.  To email everyone:

1.  Log into WebHost Manager

2. Click on ‘Email All Users’

3. Fill in the ‘from’ address, subject, and message you wish to send

4. If you wish to email the customers of your reseller accounts, check the bottom box

5. Hit ’send’, which will bring you to a confirmation page where you will need to hit ’send’ again