This document contains regulations amending a Treasury Regulation to provide guidance as to the only ways to establish prima facie evidence of delivery of documents that have a filing deadline prescribed by the internal revenue laws, absent direct proof of actual delivery. The regulations provide that the proper use of registered or certified mail, or a service of a private delivery service (PDS) designated under criteria established by the IRS, will constitute prima facie evidence of delivery. The regulations are necessary to provide greater certainty on this issue and to provide specific guidance. The regulations affect taxpayers who mail Federal tax documents to the Internal Revenue Service or the United States Tax Court.