Filing a paper tax return by regular mail can be risky.

Filing a paper tax return by regular mail can be risky. If the Internal Revenue Service doesn’t receive your tax return on time, you have the burden of proving that the return was in fact mailed on time. Your testimony that you put the return into a mailbox at the post office before the deadline isn’t enough.

Registered or certified mail, or the use of agency-approved private delivery services, are the exclusive ways by which a taxpayer can prove that tax forms were delivered to the IRS when the time of filing is in question or if the IRS can’t find a return.