You can edit the Subject line of your company's email template, 123134. 

Please know that the choices in the Insert field dropdown button will not display in the Subject line but in the body of the text. Also, the option to add the client's last name is unavailable. 

The instructions for changing the subject line above are accurate. Just make sure that the newly added template is set as the default to see the modifications when sending emails. If needed, you can also make manual edits before sending them.

You'll want to personalize the data of your sales forms. Refer to this article: Use and customize form templates.

Update me by leaving a comment below if there's anything else you need to know about handling emails in QuickBooks. I'll get back to you to share the necessary details and references. Keep safe.