Welcome to the Community! Glad to have you here. To ensure that I'm on the same page, are you wishing to send a new email to all of your customers, such as advertising a promotion? If so, you can accomplish this with the following steps:
Click Sales on the left navigation panel.
Select Customers at the top.
Place a check-mark next to the customers that you need to email.
Click the Batch actions drop-down and choose Email.