USPS Mailbox Rules: Avoid Delivery Problems

Last updated 3 months ago. Our resources are updated regularly but please keep in mind that links, programs, policies, and contact information do change.

Establishing a mailbox that meets USPS standards is the first step towards reliable mail delivery. The USPS provides specific guidelines for different types of residential mailboxes.

Curbside Mailboxes

For homes with curbside delivery, the USPS has precise regulations:

• Look for the Postmaster General’s (PMG) seal of approval on manufactured mailboxes
• Custom-made mailboxes must still adhere to PMG standards
• Present plans or custom boxes to the local postmaster for approval

Proper Placement:

• Position the bottom of the mailbox between 41 and 45 inches from the road surface
• Set back 6 to 8 inches from the curb
• Contact the local postmaster for guidance if there’s no raised curb
• Clearly display your house or apartment number on the mailbox
• If the mailbox is on a different street from your residence, include the full street address

Support Post Requirements:

• Use a stable post designed to yield if struck by a vehicle
• Recommended: 4×4 inch wooden support or 2-inch diameter standard steel/aluminum pipe
• Avoid: Heavy metal pipes, concrete posts, or other rigid supports
• Bury the post no more than 24 inches deep

Door Slots

For residences using door slots for mail delivery:

• The slot opening must be at least 1½ inches wide and 7 inches long
• Position the bottom of the slot at least 30 inches above the finished floor
• Horizontal slots: Flap must be hinged at the top and swing inward
• Vertical slots: Flap should be hinged on the side opposite the door’s hinges
• Optional mail slot hood on inside of door should not project more than 2 1/16 inches beyond the inside of the door

Wall-Mounted Mailboxes

If you prefer a wall-mounted mailbox:

• Get permission from your local postmaster before replacing a curbside mailbox
• Choose a size large enough for a normal day’s mail (letters, postcards, catalogs)
• Place near the main entrance where it’s easily visible to mail carriers
• Wall-mounted mailboxes are for postal items only, not newspapers

Commercial Mailbox Regulations

Regulations for commercial mailboxes differ from residential properties, often involving centralized mail delivery systems.

4C Horizontal Mailboxes

These are standard for new commercial and multi-unit residential buildings:

• Minimum customer compartment size: 12 inches wide, 15 inches deep, 3 inches high
• ADA compliance requirements:
  • At least one customer compartment must be less than 48 inches from the floor
  • No parcel locker compartment’s bottom shelf lower than 15 inches
  • No tenant lock higher than 67 inches
  • No customer compartment’s bottom shelf lower than 28 inches
  • USPS Arrow lock must be located between 36 and 48 inches above the floor
• Minimum ratio: One parcel locker for every five customer compartments

Cluster Box Units (CBUs)

These freestanding units are common in apartment complexes and multi-tenant settings:

• Must be installed on a concrete slab with dimensions specified by the manufacturer
• ADA compliance:
  • Mailboxes installed between 28 and 67 inches off the ground
  • At least one customer compartment no higher than 48 inches
  • Clearance of three feet in front for wheelchair access
• Arrow lock must be accessible between 36 and 48 inches from the floor
• Properties with more than ten mailboxes require at least one parcel locker per ten compartments (one per five in apartment complexes)
• Each mailbox must be clearly labeled with an apartment number or tenant name

4B+ Mailboxes

These are typically used for replacement and retrofit installations:

• Bottom row of mailboxes should be no lower than 28 inches from the floor
• Tenant locks on the top row should be no higher than 67 inches
• Master lock opening must be between 30 and 58 inches above the floor

Always contact your local postmaster before installing or replacing commercial mailboxes to ensure compliance with current regulations.

Proper Format for Addressing Mail

Correctly addressing mail is fundamental to ensuring it reaches its intended recipient without delay.

Residential Addresses

A complete residential delivery address should include:

• Recipient’s name
• Street address and number (including apartment or suite number if applicable)
• City, state (using the official two-letter abbreviation), and ZIP Code (preferably ZIP+4)
• For commercial mail receiving agencies (CMRA), include the private mailbox designator (“PMB” or “#”) and number on the line above the street address
• Use either a street address or a PO box number, not both on the same mailpiece

For optimal readability by automated mail processing equipment:

• Use all capital letters
• Avoid punctuation
• Use at least 10-point type with a simple font
• Left justify the address block
• Use black ink on white or light-colored paper
• Include a return address in the upper left corner

Commercial Addresses

The format for commercial addresses follows similar guidelines:

• Recipient’s name or company name
• Street address (including suite or floor number)
• City, state, and ZIP Code
• Optional attention line above the recipient line
• Using the ZIP+4 code is highly recommended

A complete address has all the necessary elements to allow an exact match with USPS ZIP+4 and City State files.

Keeping the Path Clear: Regulations on Mailbox Obstructions

Maintaining a clear path to your mailbox is crucial for consistent mail delivery:

• Trim overgrown vegetation (trees, bushes, vines) regularly
• Clear snow and ice from sidewalks leading to door-mounted or wall-mounted mailboxes and from around curbside mailboxes
• Ensure vehicles are not parked in a way that blocks access to curbside mailboxes
• Keep trash cans, recycling bins, and debris away from the mailbox area

If postal employees are repeatedly hindered from reaching a mailbox due to obstructions, the postmaster may withdraw delivery service until the issue is resolved. Federal law prohibits the knowing and willful obstruction of mail passage or any mail carrier.

Using Your Mailbox Flag Correctly for Outgoing Mail

For residential curbside mailboxes with a signal flag:

• Raise the flag when placing outgoing mail inside the mailbox
• This signals the mail carrier to check for outgoing mail, even if there’s no incoming mail for you
• Lower the flag once outgoing mail has been collected or if you don’t have mail to send
• USPS prefers fluorescent orange flags made of plastic (not wood) mounted on the right side of the mailbox when viewed from the front

Note that wall-mounted mailboxes, door slots, and CBUs typically don’t have flags for outgoing mail.

Package Size and Weight Limits for Standard Mailboxes

Standard residential mailboxes have limitations on the size and weight of packages they can accommodate:

• Traditional and contemporary mailbox designs must accommodate a test gauge of 18.50 inches long, 5.00 inches wide, and 6.00 inches high
• Locked mailboxes with slots must have openings large enough for standard USPS mail sizes
• The maximum mailable weight for any USPS item is 70 pounds
• For outgoing packages left in a standard mailbox with the flag raised, packages should generally be less than one-half inch thick and weigh less than 10 ounces, with correct postage affixed
• Take larger or heavier packages to a post office or schedule a pickup
• Consider installing a larger package mailbox if you frequently receive oversized packages

Prohibited Items: What You Cannot Put in Your Mailbox

USPS regulations restrict what can be placed in mailboxes:

• Only mail sent through USPS with proper postage can be placed in residential mailboxes by anyone other than postal personnel
• Unsolicited flyers or advertisements should not be placed in neighbors’ mailboxes (this rule typically doesn’t apply to mail slots on doors)

Certain items are prohibited from being sent through mail altogether:

• Hazardous materials (explosives, gasoline, liquid mercury)
• Ammunition and firearms (with limited exceptions)
• Certain perishable items and alcoholic beverages
• Common household items like flammable aerosols, lithium batteries, and nail polish have specific restrictions

Attempting to mail prohibited items can lead to penalties and compromise mail system safety.

Common Reasons for Mail Delivery Problems and How to Avoid Them

Tips for Ensuring Secure and Reliable Mail Delivery

• Regularly inspect and maintain your mailbox, ensuring it meets USPS standards
• Verify that your mailbox is clearly visible and properly placed
• Always use the correct and complete address, including the ZIP+4 code
• Keep the area around your mailbox free from obstructions
• Use your mailbox flag correctly to signal outgoing mail
• For valuable or sensitive mail, consider using USPS services that offer tracking and insurance
• Collect your mail promptly after delivery to prevent overflow and reduce theft risk

What to Do If You Experience Delivery Problems

Despite taking precautions, mail delivery problems can occasionally occur. If you experience issues:

• Track your package using the USPS Tracking tool
• Report missing mail by submitting a Missing Mail search request
• Contact your local post office (find their information on the USPS website)
• Call USPS Customer Care at 1-800-ASK-USPS (1-800-275-8777)
• File a complaint through the USPS website or contact the USPS Consumer Advocate
• Report mail theft or fraud to the U.S. Postal Inspection Service at 1-877-876-2455

Our articles make government information more accessible. Please consult a qualified professional for financial, legal, or health advice specific to your circumstances.