Thanks for getting in touch with the Community, careya2.

You can personalize emails to customers and vendors by creating and customizing a template, then using it.

Here's how:
 

1. Sign in to your books as an admin. You can also use a user account with permission to edit company preferences.
2. In the top menu bar, go to File, then Switch to Single-User Mode.
3. From your top menu bar, go to Edit, then Preferences.
4. Access the Send forms section and click its Company Preferences tab.
5. From your Delivery Method Default drop-down list, choose Email. For the Email Templates drop-down, pick a transaction type. You can create multiple templates for each transaction type listed.
6. Click Add Template and give it a name.
7. Customize your subject line and body as necessary. You can hit Insert Field to put a dynamic data field in the email. These use real data from forms, like customer name or due dates, to fill out fields.
8. When you're finished, select Save, then OK on the Company Preferences tab.

Next, you can begin using your template.

If there's any feedback or feature requests you have after using this feature, you can submit it while using QuickBooks.

I've also included a detailed resource about customizing sales forms which may come in handy moving forward: Use & customize form templates

If there's any additional questions, I'm just a post away. Have an awesome Thursday!