LetterAgent
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Address a letter with the recipient's name, street address, and city–state or province–postal code in that order, each on its own line, and put your return address in the top-left corner. Small formatting choices (where the postal code sits, how apartments are written) decide whether a sorting machine reads it or a person has to.
| Line | United States (USPS) | Canada (Canada Post) |
|---|---|---|
| 1 | Recipient's full name | Recipient's full name |
| 2 | Street address with apartment or suite on the same line (e.g. "123 Main St Apt 4") | Apartment, suite, or unit on its own line above the street (e.g. "Apt 4" then "123 Main St") |
| 3 | City, state abbreviation, ZIP code (e.g. "Springfield, IL 62701") | City, province abbreviation, then the postal code on the same line, separated by two spaces (e.g. "TORONTO ON M4B 1B3") |
| Return address | Top-left corner of the envelope, or showing through the sender window of a double-window envelope. This is what brings the letter back to you if it can't be delivered. | |
First, Canada's postal code placement: Canada Post's published standard puts the postal code on the same line as the city and province, separated by two spaces: not on its own line, the way many people write it. Second, the punctuation rule: Canada Post asks for no punctuation at all in the address block (no commas, no periods) because its scanners read cleaner without them; USPS is more forgiving. Third, the apartment split: per their published standards, USPS wants the unit designator on the same line as the street address, while Canada Post wants it on the line above. Get these three right and your letter reads exactly the way the sorting equipment expects.
The extra four digits (ZIP+4) narrow a US address down to a block or building, which helps automated sorting. But here is the catch: a wrong ZIP+4 is worse than none at all. A machine will route confidently to the wrong place, while a correct five-digit ZIP at least lands in the right neighbourhood for a human to fix. Only add the +4 if you looked it up for that exact address; guessing is not worth it.
The classics: a missing or wrong ZIP/postal code (manual handling, days added), the apartment number crammed where the scanners do not expect it, handwriting the carrier cannot read, and (the most consequential), no return address at all. Without a return address, an undeliverable letter cannot come back to you; it goes to the postal system's lost-mail office instead. Smudged inkjet printing counts too: if the barcode zone under the address is unreadable, the letter drops out of the automated flow.
Yes, in both countries: just write the box number as the delivery line ("PO Box 1234") instead of a street address. One handy USPS-specific trick: some post offices let PO box holders use the post office's street address plus their box number as the "street addressing" line, which matters when a sender's system refuses to accept PO boxes. Canada Post has its own PO box conventions: when in doubt, write exactly what the recipient gave you and do not improvise.
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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