The field [Receipt Delivery] is located on contacts and accounts. Below are their definitions.


StatusDefinition
EmailThe contact or account wants to receive tax receipts by email.

In order to receive receipts by email, the field [Email] on the contact or primary contact must be set.

If [Email] is not set, the receipt can only be mailed, regardless whether [Receipt Delivery] is "Email".
MailThe contact or account wants to receive tax receipts by mail. 

Once receipts are created, they need to be downloaded, printed and sent by mail to the donor.