The flag never went up
A letter sitting in a mailbox with the flag down looks, to the carrier, exactly like an empty box. It can sit there for days with nothing wrong except that one small metal signal.
Letters, start to finish
How to send a letter with USPS
Four things have to happen: the envelope has to be a shape USPS will take, it needs a return and delivery address, it needs a Forever stamp, and it needs to actually leave your hands. usps.com lays out that order itself, read 2026-09-01, and the last step has three separate options that most people only ever use one of.
USPS steps, citedRead 2026-09-01No stamps sold here
Envelope, stamp, drop-off
In that order. Skipping the stamp is the only step that actually stops a letter from moving.
What the envelope itself has to be
USPS sets a hard shape before anything else matters, read 2026-09-01: an envelope has to be rectangular, up to “11-1/2” long x 6-1/8” high,” and the contents have to stay “flat — no more than 1/4” thick.” A card, a folded letter, a check and most household paper goods all sit well inside that. Something bulkier, a keepsake taped in or a small object enclosed, stops qualifying as a letter and needs a different service entirely.
Postage, before the envelope is sealed
A standard envelope up to 1 oz takes one $0.82 First-Class Mail Forever stamp, per usps.com, read 2026-09-01. Go past that ounce and the piece either climbs the letter-rate ladder or, once it is heavier or stiffer than a letter, gets reclassified as a large envelope starting at $1.69 for 1 oz. A postcard is priced on its own, a $0.65 stamp rather than the letter rate.
| What you're mailing | Postage |
|---|---|
| Standard envelope, up to 1 oz | $0.82 Forever stamp |
| Large envelope, from 1 oz | Starts at $1.69 |
| Postcard | $0.65 |
One detail people miss: the Forever name means the stamp keeps working even after the price on a new one goes up, not that it covers any weight. A heavier letter still needs extra postage on top of it. Our Forever stamp price guide carries the weight ladder past 1 oz in full, and our envelope addressing guide covers exactly where the return address, delivery address and stamp go — that layout is not repeated here because it already has its own page.
Getting it out of your hands
Once it's addressed and stamped, usps.com names three ways to send it, read 2026-09-01, and none of them requires going anywhere unusual.
1
Mailbox, flag up. USPS's own wording: “Put your letter inside your mailbox and raise the flag.” The flag is what tells the carrier on the regular delivery route that there's outgoing mail to pick up along with whatever is being dropped off that day — no flag, and a carrier delivering to a full box has no reason to check for letters going the other way.
2
A blue collection box. Straight from usps.com: “Drop it in a blue collection box.” A single-ounce letter is nowhere near the limit on these, but a heavier or bulkier stamped item can be turned away — our blue collection box guide covers exactly where that line sits.
3
A Post Office lobby drop. The third option usps.com names: “Take it to a Post Office lobby drop.” This is the option for anything a collection box would reject, or simply for whoever is already walking past a branch.
Three ways a correctly addressed letter still stalls
Postage short by a fraction of an ounce
A single Forever stamp only covers the first ounce. A folded letter with an extra page or a card with something taped inside can tip past that line without feeling any heavier by hand.
Too thick for the box it went in
A padded card or anything with an object enclosed can be over the collection box's stamped-mail thickness limit even while weighing next to nothing. The fix is simply the Post Office counter instead of the corner box.
Where these rules come from
- USPS, How to Send a Letter or Postcard — envelope size, Forever stamp and postcard prices, and the three drop-off methods. Read 2026-09-01.
USPS updates its own instructions and prices without much notice. Treat the figures above as what usps.com stated on the date shown and check usps.com directly before mailing anything time-sensitive.
Common questions
How do I send a letter with USPS?
Put it in a rectangular envelope no more than 1/4 inch thick, address it with the return address top left and the delivery address bottom center, add a $0.82 Forever stamp, then get it into the system: mailbox with the flag raised, a blue collection box, or a Post Office lobby drop. That is the four-step order usps.com itself lays out, read 2026-09-01.
How much postage does a standard letter need?
One $0.82 First-Class Mail Forever stamp for up to 1 oz. A large envelope starts at $1.69 for 1 oz instead, and a postcard uses its own $0.65 stamp rather than the letter rate. All three figures are read from usps.com on 2026-09-01.
Can I just leave a stamped letter in my own mailbox?
Yes. USPS's own instructions say to put the letter inside the mailbox and raise the flag if it has one, so the carrier on the regular delivery route knows there is outgoing mail to collect along with whatever it is delivering that day.
Will any stamped letter fit in a blue collection box?
A one-ounce letter always will — it is nowhere near the limit. USPS restricts the box to stamped items of 10 oz or less that are no thicker than half an inch; anything stamped past either number has to go to an employee at a Post Office counter instead.
Does a postcard get addressed the same way as a letter?
Almost. A postcard carries the delivery address and the stamp on the same side as the message rather than on a sealed envelope, and it uses the separate $0.65 postcard rate. Everything about picking a drop-off method afterward is identical.