Any documentation of tracking is good. The USPS has many options.
Proof of mailing: .
- You can buy a Certificate of Mailing at the Post Office. A Certificate of Mailing is a proof of mailing receipt that proves you mailed your tax return/documents on a certain date. After you send your taxes/documents, keep your receipt in a safe place. The Postal Service® does not keep copies of receipts. If your return/document is delayed or lost, the postmark will not be available, but your Certificate of Mailing receipt will prove that you mailed your return/documents on time.
- These mailing services apply a postmark to your return. If your return is postmarked by the IRS deadline date, it is considered on time. Priority Mail Express, Priority Mail, First-Class Mail.
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