Hi there, @katieforster.

I can guide you in sending informative email to your customers in QuickBooks Online.

You can send an email to your customers without attaching an invoice. Just click on the Email option from the Customers tab.

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.

After that, you can select Outlook send the information that you need to your customer. You will need to have Outlook installed and set as the default email service on your computer. 

Should you need to batch send sales transactions, please refer to the following link: How to Email or Print Multiple Invoices and Sales Forms at One Time.

I'm always here to assist you further if there's anything else that you need with your customers or with QBO. Have a lovely day!