Illinois Additional Proof of Delivery (also known as iPod) is an electronic process used by the Illinois Department of Revenue to verify that a taxpayer has received certain documents from the department. iPod' documents are used to confirm that the taxpayer has received a notice of deficiency, a notice of assessment, or a notice of refund. There are two types of Illinois Additional Proof of Delivery — electronic and paper. Electronic IPODs are sent via email, while paper iPods are printed and mailed to the taxpayer. Both types of iPods contain a unique barcode or other identifying code that can be used to verify that the document was received.