In Service Manager you can automatically email invoices directly to your customers. In order to do this you need to enter a couple of settings. The first being what email address you would like the invoices sent from - for example invoices@leito.org. Secondly you need to set the text that will appear in the main body of the email.
You can also make the invoice address for new customers mandatory. To do this tick the Invoice email address required for new customers box on the settings screen.