Hi there betterlockjustin,
Thanks for reaching out about invoices. QuickBooks Online is a great tool able to help you keep track of sales and expenses so you know the profit of your company. I can provide some information about emails for customers.
There isn't a way to automate the addition of the name of your customer to the subject line of the email. it would need to be added manually before sending the transaction in question. I can see that this would be a feature that you'd like to see in the program, and I encourage you to leave feedback in the system by clicking on the Gear Icon, then Feedback. The comments made in that section are taken into consideration for new features in the software.
If you have any other questions, feel free to reach out here.
