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For tax returns and many legal deadlines, yes: the IRS treats a return postmarked on or before the deadline as filed on time, even if it arrives days later. That's the "timely mailing" rule. But it only works with a real post office postmark: your postage meter's date doesn't get the same treatment. This is general information, not tax advice.
The postmark is the inked mark the post office applies when it processes your mail: the circular date stamp over the postage. It's the post office's own record of when the item entered its system, which is why courts and agencies trust it. Not every date-like mark on an envelope qualifies.
| Mark on the envelope | Counts as the mailing date? | Why |
|---|---|---|
| USPS postmark | Yes | Applied by the post office; independently verifiable |
| Canada Post postmark | Yes, for CRA deadlines | Same principle; check CRA's specific rules |
| Private postage meter date | No, for IRS timely-filing purposes | You control the meter, so the date isn't independently verified |
| Shipping label or online postage date | Not the same thing | Shows when the label was printed, not when the post office got it |
This is the trap. A postage meter prints a date on your envelope, and it looks official, but you set that date yourself: you could print tomorrow's date or last week's. The IRS knows this, so for the timely-filing rule it generally uses the date the return was actually received when the envelope bears only a private meter mark. Plenty of taxpayers have learned this the expensive way, assuming their meter date protected them.
The practical rule: if a deadline matters, get the letter postmarked at the post office counter and ask for a receipt. Better yet, send it certified mail: the certified receipt is dated, and it proves both when you mailed it and that the post office accepted it.
Keep the certified mail receipt, which shows the mailing date stamped by the post office. Photograph the envelope showing the postmark before you mail it, though the photo is backup rather than proof. And keep a copy of what you sent: if the return itself goes missing, you'll need to reproduce it fast, and the copy plus the mailing receipt together tell the whole story.
Many states mirror the federal timely-mailing rule, but not all, and the details vary: which marks count, which deadlines are covered, what happens with electronic filing. If you're dealing with a state tax deadline rather than a federal one, check your state's rule instead of assuming the IRS logic carries over. When the stakes are real, a tax professional's confirmation costs less than a missed deadline.
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