Mailing basics
How to mail a letter, step by step
Mail a letter in six steps: address the envelope, add your return address, seal it, put a Forever stamp in the upper-right corner, and drop it at a mailbox.
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Plain answers about postage, addresses, and Certified Mail, plus better ways to connect your business to the mailbox. Practical ideas for paper, code, and the people behind both.
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Send a custom postcard with the IRIS REST API
Prepare separate postcard print faces, register the PDFs, quote a US order, and submit only after reviewing the artwork, addresses, and price.
Explore the mailing APILatest articles
73 articles
Mailing basics
How to fold a letter for an envelope
Fold a letter into thirds for a No. 10 envelope, use a Z-fold so the address shows in a window envelope, or fold in half for cards and smaller envelopes.
Mailing basics
Envelope sizes: a chart of standard US envelopes
See standard envelope sizes in one chart: No. 10 business envelopes, A2 to A9 card sizes, 9 × 12 catalogs, and squares, plus which sizes mail with one stamp.
Mailing basics
What is Certified Mail, and why would you get a certified letter?
Certified Mail is a USPS add-on that gives the sender a mailing receipt and a signed delivery record. Learn what it looks like, who sends it, and what to do.
Mailing basics
How to send Certified Mail, step by step
Send a certified letter: fill out PS Form 3800, add the green label, choose a Return Receipt, pay $5.55 plus postage, and keep the receipt to track delivery.
Mailing basics
Certified Mail vs. Priority Mail: which one do you need?
Certified Mail is a $5.55 add-on that records a signed delivery; Priority Mail is a 2–3 day class with tracking and insurance. Compare costs and combinations.
Mailing basics
What is First-Class Mail? What it covers, costs, and how it compares
First-Class Mail is USPS’s service for letters, postcards, and flats up to 13 oz: $0.82 letters, $0.65 postcards, 1–5 days. What qualifies and how it compares.
Mailing basics
What is a mailing address, and how is it different from a physical address?
A mailing address is where you receive mail. It’s often your physical street address, but can be a PO Box, private mailbox, or General Delivery. With examples.
Mailing basics
Postcard sizes: standard dimensions, USPS rules, and print setup
The standard US postcard size is 4 × 6 inches. See common postcard dimensions, which sizes mail at the $0.65 postcard price, A6 vs A5, and bleed for print.
Mailing basics
Where to mail your federal tax return, and how to make sure it counts as on time
Mail a paper 1040 to the IRS address for your state and payment status. Extended 2025 returns are due Oct. 15, 2026; a timely postmark makes them on time.
Mailing basics
USPS holiday mailing deadlines for 2026: when to send cards, letters, and gifts
Mail Christmas cards by Dec. 17, 2026 for USPS delivery by Dec. 25. See all 2026 USPS holiday deadlines, plus military, international, and Christmas Eve mail.
Mailing basics
How to mail a check safely, and what to do if it goes missing
Mail a check safely: black ink, no blank spaces, a security envelope, and a Post Office drop. Add Certified or Registered Mail and watch it until it clears.
Mailing basics
USPS Operation Santa 2026: Santa’s address, key dates, and how to adopt a letter
Write to Santa, 123 Elf Road, North Pole, 88888, and mail it by December 5, 2026. See USPS Operation Santa dates, letter rules, and how to adopt a letter.
Business mail
When are 1099s due? Deadlines for 2026 forms, filed in 2027
Most 2026 1099s are due to recipients February 1, 2027, as is 1099-NEC to the IRS. See paper and e-file dates, where to mail Form 1096, and the new $2,000 rule.
Mailing basics
How much is a book of stamps in 2026?
A book of 20 Forever stamps costs $16.40 at USPS prices since July 12, 2026, or $0.82 a stamp. See coil, sheet, postcard, and Global Forever prices and history.
Mailing basics
Where to buy stamps: Post Office, online, and stores
Buy stamps at a Post Office or kiosk, at The Postal Store online, by phone or mail, or at stores. Prices, markups, and how to avoid fake discount stamps.
Mailing basics
Does USPS deliver on Sunday? What arrives, and what waits until Monday
USPS doesn’t deliver regular mail on Sunday; only Priority Mail Express and Amazon parcels arrive. See Saturday delivery, Post Office hours, and holiday rules.
Mailing basics
USPS lost mail: how to find a missing letter or package and file a claim
USPS lost mail? Start a Missing Mail search 7–365 days after mailing, file an insurance claim if covered, and report theft to Postal Inspectors.
Mailing basics
How to fill out a money order, step by step
Fill out a money order step by step: payee, purchaser, memo, signature, receipt stub. Plus USPS fees ($2.65–$3.75), the $1,000 limit, cashing, and replacement.
Mailing basics
How to write a letter: format, examples, and how to start and end
How to write a letter: the parts in order, formal vs. informal format, how to start and end, short examples, and how to proofread, address, and mail it.
Business mail
Business letter format: block, modified block, and a full example
Business letter format, explained: full block, modified block, and semi-block layouts, each part in order, a complete example, and how to mail it with proof.
Mailing basics
USPS change of address: how to file, what it costs, and who else to tell
Change your address with USPS online for $1.25 or free at a Post Office, see how long mail is forwarded, avoid look-alike sites, and know who else to tell.
Mailing basics
How much is a PO Box? 2026 USPS fees by size and term
How much is a PO Box? USPS fees run $21–$98 for 3 months for the smallest box, set by size and fee group. See every size, 12-month cost, keys, and free boxes.
Mailing basics
USPS Informed Delivery: sign in, what it shows, and why mail is missing
Sign in to USPS Informed Delivery, see what it shows, and learn why some mail isn’t pictured. It’s free, needs ID verification, and previews letter-size mail.
Mailing basics
How to write a check: step by step, with cents, endorsing, and voiding
How to write a check: each part labeled, every step in order, writing cents as a fraction, filled-in examples, and how to endorse a check or void one.
Business mail
How to write a resignation letter: what to include, examples, and notice
A resignation letter states that you’re leaving, your last day, thanks, and a handoff offer. See examples, notice norms, what to leave out, and how to send it.
Mailing basics
What does Esq. mean? Esquire vs. attorney, and how to address a lawyer
Esq. meaning: a courtesy title for US lawyers, not a degree or license. Esq. vs. J.D. vs. attorney, the Mr./Ms. rule, and how to address a letter to a lawyer.
Mailing basics
Cease and desist letter: what it is, what to include, and how to send it
What a cease and desist letter is, when it has legal force, what to include, a fictional example, and how to send it by Certified Mail so you can prove it.
Mailing basics
Global Forever stamp: price, what it covers, and how to mail a letter abroad
A Global Forever stamp costs $1.75 and mails a 1-ounce letter or postcard to any country. Prices for heavier letters, Canada, customs rules, and addressing.
Mailing basics
What is a ZIP Code? Meaning, ZIP+4, and how to find yours
What is a ZIP Code? What ZIP stands for, what each digit means, how ZIP+4 works, how to find yours with USPS, and how ZIP Codes differ from postal codes.
Mailing basics
How to address a postcard: where the address, stamp, and message go
How to address a postcard: stamp in the top-right corner, address on the right, message on the left, plus a fictional example, size rules, and postage.
Mailing basics
What does ATTN mean? How to use an attention line on mail
ATTN means “attention.” Learn where the attention line goes on an envelope per USPS, how to address a letter to a company or department, and ATTN vs. c/o.
Mailing basics
Thank you letter: how to write one, with examples for every occasion
How to write a thank you letter: the parts in order, when to send it, examples for gifts, interviews, donors, and sympathy, and how to mail a card or note.
Mailing basics
Demand letter: what to include, deadlines, and how to send one
What a demand letter is, when to send one before small claims, what to include, deadline wording, a sample letter, and how to mail it with Certified Mail.
Mailing basics
USPS General Delivery: what it is, how to use it, and how to address it
USPS General Delivery holds mail at a Post Office for people without a permanent address. Learn who can use it, the address format, hold times, and pickup ID.
Mailing basics
USPS Form 1583: how to fill out, sign, and verify ID for a private mailbox
USPS Form 1583 lets a mail store or virtual mailbox receive your mail. Learn who signs, which two IDs count, notary and video options, and how to write a PMB.
Mailing basics
Character letter for court: how to write a letter to a judge, with an example
How to write a character letter for court: what to include, what to leave out, how to address the judge, how to submit it, and a fictional sample letter.
Mailing basics
How to write a condolence letter: what to say, examples, and when to send it
How to write a condolence letter: when to send it, what to say, examples for friends and coworkers, phrases to avoid, belated notes, and how to mail it.
Mailing basics
How to stop junk mail: opt-out lists, credit card offers, and what you can’t stop
How to stop junk mail: opt out of credit card offers, register with DMAchoice, contact senders, and handle Current Resident, refused, and deceased mail.
Mailing basics
USPS Hold Mail: how to pause your mail for 3–30 days
USPS Hold Mail keeps your mail at the Post Office for 3–30 days, free. How to request it online or in person, deadlines, pickup, changes, and longer options.
Mailing basics
How to cancel PMI: when it goes away and how to request removal
How to cancel PMI: request it in writing at 80% of original value, automatic removal at 78% or the midpoint, an LTV example, and how FHA MIP differs.
Mailing basics
How to write a letter to the president: White House address, format, and example
How to write a letter to the president: the White House mailing address, the online contact form, what to include, tone, length, and a short sample letter.
Mailing basics
Security deposit demand letter: when to send it, what to include, and an example
Learn when to send a security deposit demand letter, state return deadlines, what to include, a sample letter, and how to mail it with Certified Mail proof.
Mailing basics
30-day notice to landlord: how to write one, with an example
Learn how to write a 30-day notice to your landlord: when it’s required, state examples, what to include, how to count the days, a sample, and how to mail it.
Mailing basics
How much does Certified Mail cost in 2026?
Work out what a certified letter costs after the July 12, 2026 USPS price change: postage, the $5.55 fee, Return Receipt options, and worked totals.
Mailing basics
Registered Mail vs. Certified Mail: which one do you need?
Compare USPS Registered Mail and Certified Mail on security, insurance up to $50,000, tracking, signatures, 2026 fees, and speed before you choose one.
Mailing basics
Can you send Certified Mail to a PO Box?
Certified Mail can go to a PO Box. See how the pickup notice, counter signature, 15-day hold, and Restricted Delivery work, and when to use a street address.
Mailing basics
How to address an envelope: a line-by-line USPS guide
Address an envelope the USPS way: where the recipient, return address, and stamp go, what each line holds, and examples for apartments, businesses, and APO.
Mailing basics
How to write a PO Box address, with examples
Write a PO Box address USPS can deliver: PO BOX and the number above the city, state, and ZIP Code, plus examples, line 1 vs. line 2, and Street Addressing.
Mailing basics
What does c/o mean in an address? How to use “care of”
C/O means “care of.” See where the c/o line goes in an address, examples for guests, children, clients, and businesses, and when ATTN is the better choice.
Mailing basics
Returned to sender: what USPS return reasons mean and how to fix them
Find out why USPS returned your mail, what endorsements such as Insufficient Address or Unclaimed mean, and how to correct the address before you mail it again.
Mailing basics
How much does it cost to mail a letter in 2026?
See what it costs to mail a letter in 2026: one $0.82 Forever stamp covers 1 oz, each extra ounce is $0.29, and square or rigid envelopes add $0.49.
Mailing basics
How much is a postcard stamp in 2026?
A postcard stamp costs $0.65 from July 12, 2026. Check which card sizes qualify, what a 5 × 7 or square card costs, and how to address and stamp a postcard.
Mailing basics
USPS holidays 2026: Post Office closures and mail delivery days
See each 2026 USPS holiday with date and weekday, what closes, whether there is mail delivery today, and how holidays affect First-Class delivery times.
Mailing basics
Every Door Direct Mail (EDDM): how it works, what it costs, and when addressed mail fits better
See how USPS Every Door Direct Mail works, what EDDM costs per piece in 2026, its size and quantity rules, and when individually addressed postcards fit better.
Mailing basics
USPS Certificate of Mailing: what it proves, what it costs, and how to get one
Learn what a USPS Certificate of Mailing proves, what PS Form 3817 costs from July 12, 2026, how to get one, and when Certified Mail is the better choice.
API & development
Send a custom postcard with the IRIS REST API
Prepare separate postcard print faces, register the PDFs, quote a US order, and submit only after reviewing the artwork, addresses, and price.
AI assistants
Find and use an MCP server for physical mail
A client-neutral guide to the IRIS physical-mail MCP endpoint, its six tools, private PDF transfer, least-privilege scopes, and the approval boundary before a paid mailing.
AI assistants
Prepare a Letter for Mailing with Grok and IRIS
Connect Grok to IRIS through a custom MCP connector for bounded preparation, transfer the final PDF privately with trusted code, and require human approval before any paid mailing.
AI assistants
Prepare and Quote a Letter with OpenClaw and IRIS MCP
Register IRIS as an authenticated OpenClaw MCP server, prepare and quote a letter with limited permissions, then require a separate human-approved submission.
AI assistants
Use Meta Muse to prepare a letter, then review it before mailing
Use Muse as a browser-assisted guide for a reviewed PDF mailing through IRIS, or connect Muse Code to the IRIS MCP server for a developer workflow.
API & development
A print and mail API: from your software to their mailbox
Understand the PDF-to-mail workflow, what your application owns, and how to choose an integration for individual business letters.
AI assistants
Mail documents with Claude Code and the IRIS MCP server
Connect Claude Code to IRIS, prepare a private PDF, review the quote, and submit an individual letter through authenticated MCP tools.
AI assistants
From ChatGPT draft to a real letter in the mail
Two ways to turn an AI-assisted draft into physical mail: a reviewed PDF upload or a custom application built with OpenAI and the IRIS API.
AI assistants
Give your AI agent a mailing workflow you can trust
Design the handoff from an agent-prepared document to a human-approved mailing, with limited credentials and a durable record of every send.
API & development
Prepare a PDF mailing with Python and the IRIS API
A Python preparation script for private PDF uploads, document registration, and a mailing quote, with a separate review step before submission.
API & development
Prevent duplicate letters when an API request times out
Use a durable mailing intent and one saved idempotency key to handle retries, duplicate events, and uncertain responses without ordering another letter.
Business mail
Automate invoice mailing without rebuilding your billing system
Turn a finalized invoice PDF into a reviewed paper mailing, while keeping balances, payment instructions, and customer preferences in your billing system.
Business mail
Turn a CRM event into a useful customer letter
Build an event-to-letter workflow for individual customer correspondence, with clear ownership, deduplication, and a review before each mailing.
Business mail
Create and Mail a Client Welcome Packet as One PDF
Plan a concise welcome packet, combine its pages into a finished PDF, and mail it as one letter after your team reviews the recipient and next steps.
Business mail
Send Business Notices with Certified Mail and the IRIS API
Match a business letter to the mailing record you need, compare Certified Mail and Return Receipt, and preserve document and order references in your app.
Business mail
Build an outbound mailroom for your remote team
Build an outbound mailroom with the IRIS API. Compare mailroom types, prepare and review letters, recover safely from retries, and track individual US mailings.
Business mail
Make service renewal letters easier to act on
Prepare clear renewal correspondence from approved account details, check it against recent changes, and send an individual letter through the IRIS API.
From the team behind IRIS
Useful before you send.
Published by IRIS Postal Forms, operated by Great Lakes Computing Office LLC. Our articles explain our mailing tools and practical business workflows, with sources for product and platform details. Examples are illustrative, and publication dates reflect when an article was added.
Start with our mailing guides for everyday questions, or contact us about a correction.
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