Whether you're moving to a new address, setting up a P.O. box, or dealing with apartment mail delivery, you may come across the term mailbox number. While it might seem like a simple concept, understanding what a mailbox number is — and how it's used — is essential for accurate mail delivery, privacy, and efficient communication.
In this article, we’ll explain what a mailbox number is, why it’s important, how to locate it, and where it fits in various mailing systems — from residential homes to apartment complexes and commercial settings.
What Is a Mailbox Number?
A mailbox number is a unique identifier assigned to a specific mailbox. It helps mail carriers, delivery services, and residents locate the correct mailbox for a given person or address. This number can be part of a physical address or separate from it, depending on the type of mailbox system in place.
In most cases, a mailbox number appears on or near the mailbox and may also be used when addressing letters or packages to ensure proper delivery.
Where Are Mailbox Numbers Used?
1. Apartments and Condominiums
In apartment buildings or condo complexes, individual units typically do not have street-facing mailboxes. Instead, all residents share a central mail center where each tenant is assigned a specific mailbox number. In this case, the mailbox number does not always match the apartment number — a common source of confusion.
2. Post Office Boxes (P.O. Boxes)
A P.O. box is a secure mailbox located within a post office. When you rent a P.O. box, you're given a mailbox number, which often looks like this:
John Doe
P.O. Box 12345
City, State ZIP
The mailbox number here is 12345, and it is necessary for accurate mail routing.
3. Commercial Mailboxes
Businesses that receive a high volume of mail may use commercial mailbox services (e.g., UPS Store mailboxes). These services assign each client a mailbox number for identification purposes. It often appears in the address as a # symbol or the abbreviation PMB (Private Mailbox), like this:
ABC Company
123 Main St. PMB 456
City, State ZIP
4. Gated Communities and Shared Mail Centers
Some gated communities or subdivisions have cluster mailboxes for several homes. Residents are assigned a box number distinct from their house number. It's critical to include this number in your address to avoid lost or delayed mail.
Why Is a Mailbox Number Important?
The mailbox number plays a key role in mail sorting and delivery. Here’s why it matters:
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Accuracy: It ensures the mail reaches the correct recipient.
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Efficiency: Speeds up delivery by helping postal workers and couriers locate your box.
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Privacy: Especially in shared spaces, it prevents mail from being mixed up or misdelivered.
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Consistency: Mail systems depend on reliable identifiers like mailbox numbers to operate effectively.
Failing to include a mailbox number — or using the wrong one — can lead to returned mail, missed deliveries, and other logistical issues.
How to Find Your Mailbox Number
If you’re unsure of your mailbox number, here are some ways to find it:
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Lease or Rental Agreement: Apartment complexes usually list the mailbox number in your lease paperwork.
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Property Manager or Landlord: They can confirm your assigned mailbox.
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Mailbox Itself: Look for a labeled number on or inside the box.
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Post Office: For P.O. boxes, the number is provided when you rent the box.
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Commercial Provider: If using a UPS Store or similar service, the mailbox number will be part of your rental agreement.
How to Format an Address with a Mailbox Number
Proper formatting depends on the type of mailbox:
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Apartment mailbox:
Jane Smith
456 Elm St., Apt 5B, Mailbox 32
City, State ZIP -
P.O. Box:
Jane Smith
P.O. Box 7890
City, State ZIP -
Private Mailbox (PMB):
Jane Smith
789 Market St., PMB 210
City, State ZIP
Avoid using ambiguous formats like simply writing "#210" without context, especially if USPS delivery is involved.
Is a Mailbox Number the Same as an Apartment Number?
Not always. This is a common misconception. In many apartment complexes, the mailbox number is different from your unit number. For example, you might live in apartment 7C but your assigned mailbox could be box 12.
Always double-check to avoid mix-ups and notify your contacts of the correct mailbox number to use.
Mailbox Numbers and Online Forms
When filling out forms online — for billing, subscriptions, or deliveries — you may be prompted to include a mailbox number. This is especially common for:
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Apartment deliveries
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Business registrations
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E-commerce accounts
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Shipping and logistics portals
Be precise and consistent with your input. Mistakes in your mailbox number can result in misrouted or lost mail.
FAQ: What Is a Mailbox Number?
Q: Is a mailbox number required in all addresses?
A: No, standalone homes usually don’t have separate mailbox numbers. They use the street address. Mailbox numbers are common in apartments, condos, and P.O. boxes.
Q: Can I make up my own mailbox number?
A: No. Your mailbox number is assigned by the property manager, post office, or mailbox provider. Using an unassigned number can lead to delivery errors.
Q: Is the mailbox number the same as a ZIP code?
A: No. A ZIP code identifies a geographic area, while a mailbox number identifies an individual mailbox within a building or facility.
Q: What happens if I leave out my mailbox number?
A: Your mail may be delayed, returned to the sender, or delivered to the wrong person. Always include the correct mailbox number for accurate delivery.
Q: Where should I write my mailbox number in my address?
A: It depends on the mailbox type. Use formats like “PMB 123”, “P.O. Box 1234”, or include “Mailbox 45” in the second address line.