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Read the endorsement on the returned envelope: the yellow USPS sticker or Canada Post label tells you why it came back. Usually the address was wrong, the recipient moved, or the unit number was missing. Fix the address, then mail a fresh letter. A returned letter was never delivered, so the fix that matters is getting the address right.
The sticker on your returned envelope isn't decoration: it's the post office telling you exactly what went wrong. Here's how to read the common ones.
| Endorsement | What it means | What to do |
|---|---|---|
| Undeliverable as addressed | The address couldn't be matched to a delivery point | Verify the full address with the recipient |
| No such address | The street number or street name doesn't exist | Check spelling and numbering; look it up on a map |
| Insufficient address | Missing apartment, suite, or unit number | Get the secondary number and add it |
| Moved, left no address | Forwarding expired or no forwarding was ever filed | Find the recipient's current address |
| Refused | The recipient declined to accept it | They chose not to take it; try another channel |
| Unclaimed | Notices were left but it was never picked up | Resend, or reach them another way first |
A missing apartment or suite number is the most common cause, and it fools people because the address looks complete without it. A street address with no unit number often can't be delivered in an apartment building or office complex, so the whole letter comes back.
Another sneaky one: window envelopes. If the letter shifts inside the envelope during handling, a different line can show through the window: the post office reads whatever is visible, and if that's a partial address or the return address, the letter gets misrouted or returned. Tightly folded letters in correctly sized envelopes shift less.
New construction is a third cause. If the building is very new, it may not be in the postal database yet, and automated systems reject addresses they can't verify. In that case the recipient's local post office can confirm the delivery point exists.
Don't just drop the same envelope back in the mail: it will come back again. Verify the address with the recipient directly, by phone or email, and read it back to them including the unit number. Then check it against the post office's own lookup tool: USPS ZIP Code lookup for US addresses, or Canada Post's address tools for Canadian ones. If the lookup can't find it, the post office probably can't deliver to it either.
If you mailed through LetterAgent, remember the sender's address shows through the envelope's second window and acts as the return address, so undeliverable mail comes back to you rather than disappearing. That return is working as designed: it's your signal to fix the address.
Usually not. A returned letter wasn't delivered, so for legal or tax deadlines it generally doesn't count as sent or served: what matters is getting a delivered letter to the right address before the deadline. Keep the returned envelope unopened as evidence of when you first tried. This is general information, not legal advice.
Ready to mail it? Send your letter with LetterAgent: describe it to your AI assistant, approve the exact quoted price, and it's printed and mailed.
LetterAgent is a working name. Prices include print, postage, and our service fee. US prices in USD, Canadian prices in CAD (Canadian prices exclude applicable sales tax, added at checkout). Currently in private testing.
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