A postmark is a postal cancellation mark applied to the address side of a stamped letter, flat, or parcel. Its core functions are:
Historically, postmarks were applied by hand using metal or rubber ink stamps. Today, high-speed automated sorting machines process the vast majority of mail, applying printed digital cancellations at speeds of tens of thousands of letters per hour. The Legal and Financial Importance of the Postmark postmark
Ironically, as we rely on email, the physical postmark has become more valuable specifically because it is physical. Email headers can be spoofed; "Sent" times can be manipulated by changing a device's clock. But a physical ink postmark is incredibly difficult to fake without access to heavy-duty industrial printing equipment. A postmark is a postal cancellation mark applied
However, as of late 2025 and moving into the 2026 tax season, the U.S. Postal Service (USPS) has finalized new rules that fundamentally alter this familiar process. For taxpayers and voters, this means a "postmark" can no longer be blindly trusted as the date you handed your mail to a postal worker. The Legal and Financial Importance of the Postmark
Postmark operates on a strict "no-bulk-mail" policy. They actively ban spammers and cold emailers. Because their sending IPs aren't polluted by cheap affiliate offers, Internet Service Providers (ISPs) trust them.