How to address an envelope

📮 Apartment or suite number

Include the unit number at the end of the street line, on the same line, not on a separate line below it. Use standard abbreviations: APT for apartment, STE for suite, UNIT for unit. Avoid the # symbol, since it can be misread by optical scanners. If the full address is too long for one line, place the unit number on a separate line directly above the street line, never below. The USPS reads the line immediately above the city as the delivery point, and a unit number below the street line gets misread as part of the city name.

📦 PO Box

Replace the street address line entirely with the PO Box number. Do not include both a street address and a PO Box on the same envelope. If both appear, USPS defaults to the street address, which is often not where the PO Box holder receives mail. Use the ZIP code assigned to the PO Box, which may be different from the ZIP code for the physical post office at the same address.

🏢 Business address

The person’s name goes on line 1. The company name goes on line 2. Street address on line 3. City, state, ZIP on line 4. If you do not know a specific person’s name, put the department or role on line 1 ("Hiring Manager" or "Billing Department") and the company name on line 2. Do not put a job title on the same line as the name — that line is for honorifics and the full name only.

📋 ATTN line

Use ATTN when you need mail routed to a specific person within a company or organization that handles high mail volume. The ATTN line goes directly above the company name, not above the street address. Format: ATTN JORDAN REYES, no colon required, no punctuation. Without it, high-volume mail facilities often deliver to a central mailroom with no further routing.

📨 C/O (Care Of)

Use c/o when the recipient does not permanently live or work at the address, and is receiving mail through someone else. Place the c/o line on line 2, below the recipient’s name and above the host’s name or street address. This is different from ATTN: c/o routes mail through an individual, ATTN routes mail through an organization.

💍 Married couple

For informal mail — cards, invitations — use both first names with the shared last name on one line: "David and Laura Mitchell." For formal mail, include titles: "Mr. David Mitchell and Mrs. Laura Mitchell." If they have different last names, always use two lines, one name per line. The rule is simple: one line per last name.

👨‍👩‍👧 Family

"The [Last Name] Family" is acceptable for cards and informal mail — it is inclusive and covers everyone at the address without listing names. For formal correspondence, address the adults individually by name. Children at the same address are generally not included on the envelope unless the correspondence is directed at them specifically.

👩‍⚕️ Professional titles (Dr., Esq., Rev., Ph.D.)

Place professional titles before the name (Dr., Rev., Prof., Hon.) or after it (Esq., Ph.D., M.D.), never both at once. "Dr. Jane Smith" and "Jane Smith, M.D." are both correct. "Dr. Jane Smith, M.D." is redundant, so pick one form. Never combine Mr. or Ms. with a professional title: an attorney who is a woman is "Jane Smith, Esq.", not "Ms. Jane Smith, Esq."

🌍 International mail

The three zones — return address top-left, delivery address centered, stamp top-right — are the same. The key addition is the final line: write the destination country name in English, in all capital letters, alone on the last line. Do not abbreviate. Some countries have different postcode formats and internal line orders, but the country always goes last regardless of their convention. Do not include your own country on mail sent from within it.

🪖 Military mail (APO / FPO / DPO)

Military addresses use APO (Army/Air Force Post Office), FPO (Fleet Post Office), or DPO (Diplomatic Post Office) in place of the city name. The two-letter state equivalent is AA, AE, or AP depending on the region. The ZIP code is a 9-digit military ZIP. Treat military mail exactly like domestic mail: no country name on the envelope, domestic postage rates apply.

📬 Without a return address

Standard mail can legally be sent without a return address. If delivery fails, however, the piece is disposed of rather than returned to you, since there is nowhere to send it back to. A return address is required for Certified Mail, Priority Mail Express, and all international mail. For everything else, omit it only if you are certain the delivery address is correct and you do not need the letter back if something goes wrong.