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Yes. Your old stamps still count, so you only need to cover the shortfall, not pay the full postage again. Cross out the yellow or orange return endorsement so it is clearly defaced, affix enough additional stamps to reach the correct amount, and drop the same envelope back in the mail. The envelope is reusable as long as the address and postage are legible.
That depends on where USPS caught the shortfall. If it is spotted at the originating post office, the letter comes straight back to you with a return endorsement. If it makes it all the way through processing, it may instead be delivered postage due, meaning the recipient pays the difference plus a small handling fee. You get whichever outcome the facility that noticed it applied.
The return endorsement usually does not say the exact shortfall, so weigh the letter and check the current rate table yourself. The most common causes: an envelope that weighed more than one ounce, a square or unusually shaped envelope (square envelopes pay a nonmachinable surcharge because they cannot run through the automated sorters the same way), or a rigid enclosure that pushes it into a higher class. Fix the real cause, not just the stamps.
| Condition | OK to remail? |
|---|---|
| Original stamps uncanceled and readable | Yes, they still count toward postage |
| Return endorsement crossed out | Yes, required so the letter is not bounced again |
| Envelope torn open at the flap | Reseal it cleanly with tape; contents must not spill |
| Original stamps were canceled | The envelope still works, but those stamps no longer count |
| Address smeared or the window is damaged | Move the contents to a fresh envelope and reapply all postage |
Yes, and this is the most reliable move. Bring the returned envelope to the counter and ask the clerk what it needed. They will weigh it, name the correct class, and sell you exactly the right stamps. That one trip prevents a second return, which matters because every bounce costs you several days.
Largely, yes. Canada Post also returns underpaid mail to the sender with an endorsement, and you remail by adding stamps to make up the difference. One Canadian wrinkle: if the return address is missing or illegible, underpaid mail can end up at the Undeliverable Mail Office instead of coming back to you, and retrieving it takes considerably longer. Keep the return address legible so the letter can find its way home.
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