You can email some customer invoices and print for others.
The email address for the customer is the key. The "Include Customers without E-Mail Address" option will cause the system to send e-mail for ALL customers, even if the customer does not have an email address entered in their customer setup. When this option is turned on, all email for customers without an e-mail address will be sent to your return e-mail address, alerting you that this customer has an empty email address in their customer setup. If this option is turned OFF, customers without an email address will NOT be sent. They will not be marked as printed either, so you will need to run the batch print option to print out these remaining invoices. This allows you to have some customers who receive their invoices (or statements) by email and some customers who have their invoices (or statements) printed and mailed. This is a powerful option which allows you to interact with your customers by postal mailing their invoices, while trying to save money on postage costs by sending email to your customers who have an email address.