LetterAgent
Mail physical letters by just asking your AI assistant.
ZIP+4 is the nine-digit ZIP code: the usual five digits plus four more that narrow delivery to a segment as small as one side of a block or one floor of a building. Five digits deliver fine. The extra digits speed up automated sorting. Canada has no ZIP+4 equivalent: the seven-character postal code is required.
The five-digit ZIP gets your letter to the right post office. The +4 narrows it to a delivery segment inside that area: one side of a city block, a single large building, one floor of an office tower, or a group of PO boxes. Introduced in 1983, the system exists so sorting machines can route mail closer to its final stop without human help. A nine-digit code can pinpoint a single apartment building, which is why bulk mailers love it and why you have probably seen it on junk mail.
| Five-digit ZIP | ZIP+4 (nine digits) | |
|---|---|---|
| Gets delivered | Yes, always | Yes, always |
| Sorting speed | Normal automated sorting | Slightly faster automated sorting, fewer manual touches |
| Required for | Everything | Nothing a regular sender does; some bulk-mail discounts require it |
| Where to find it | On any address | USPS ZIP code lookup, or printed on mail you have received from that address |
For a personal or business letter, five digits are enough. Add the +4 when you know it, since it costs nothing and helps the machines, but never hold up a letter to look one up. A correct five-digit ZIP beats a guessed nine-digit code: a wrong +4 can send your letter to the wrong segment and slow it down more than no +4 at all.
Five digits, a hyphen, four digits: 90210-1234. No spaces around the hyphen. It goes in the same place the ZIP always goes, at the end of the city, state line. Do not put the +4 on its own line or in parentheses; the hyphenated form is what the readers expect.
There isn't one, because Canada's postal code already does the job. The seven-character code (letter-number-letter, space, number-letter-number, like M4B 1B3) narrows delivery down to a small area on its own, and the full code is required on every address, not optional. The last three characters, called the local delivery unit, play a role similar to the +4: they can identify one side of a block or a single building. Canada Post wants the postal code on the same line as the city and province, with two spaces between the province and the code.
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.
Need help? Ask your assistant. It can check a job's status any time. If it ever can't handle something: hello@getletteragent.com