For added peace of mind, you can buy a Certificate of Mailing at the Post Office. If your return is delayed or lost, a Certificate of Mailing is a proof of mailing receipt that proves you mailed your tax return on a certain date. (After you send your taxes, keep your receipt in a safe place. The Postal Service does not keep copies of receipts).
Also, when you use a USPS service with tracking, your tracking number will provide updates as your item travels to its destination, including the date and time of delivery or attempted delivery. You can access tracking information for non-signature items for 120 days (2 years for signature items). With the USPS Tracking Plus ® service, you can buy extended tracking history for up to 10 years.
These mailing services apply a postmark to your return. If your return is postmarked by the IRS deadline date, it is considered on time. With Click-N-Ship ® service, you can pay for postage online and print a shipping label from your own computer. Generating a Click-N-Ship label with postage creates an electronic record for the label on that specific date, so it is important that you send your package on the shipping date you used to create the label. Your online Click-N-Ship account will save your shipping history for six months.
The Postal Service recommends that you confirm all tax information with a tax professional or the IRS.
