Do you want the ability to automatically send customers a copy of their receipt? You can with Unit Trac. 

Step 1 - Go to Business > Settings > Notifications

Step 2 -  Review which settings you would like to enable to communicate with your customers. 

After enabling the settings, don't forget to click "Manage" to select your current customers.

For more info on customizing invoices see; add your logo, or add custom notes.