Send an email message to all users in Salesforce.
Setup > Manage Users > Mass Email Users
Click Go to get the list of all the users. You can also create New View and filter the users as required.
Now we have to select an email template. Email templates can be found and selected from the folders.
Enter the Mass Email Name.
Delivery Options: When you want to schedule the email. You can send the email right now by selecting Send now option or you can schedule the mass email on specific date and time and time zone.
Email sent to all the selected users and click finished.
We also receive the status of mass email in our email account.