I would like to send an e-mail to all my customers letting them know of a rate change. Can I send a customized e-mail to every customer on my list at the same time?

Hello there, @lindak1119.

You can customize and send an email to your customers in QuickBooks Online,

Here’s how.

1. Click Sales on the left navigation panel.
2. Select Customers at the top.
3. Place a check-mark next to the customers that you need to email.
4. Click the Batch actions drop-down and choose Email.

Please know that you will need to have Outlook installed and set as the default email service on your computer. 

You can also check out this article as future reference if you need to email and customize sales form: Customize sales form.

Let me know if you need further assistance. Have a nice day!