Must Mailboxes Have Flags? (Explained)

Mailbox flags are very important to our mail carrier system. However, they aren’t always necessary.

Here’s what you need to know about mailbox flags:

Here’s Why Mailboxes Don’t Always Need Flags:

Mailbox flags are only used in the United States Postal Service (USPS) for Full-Service mailboxes. Mailboxes used in neighborhoods and residential communities throughout the United States are full service. Therefore, not all mailboxes need flags, though most residential mailboxes should have one.

Why Do Some Mailboxes Have Flags?

The mailbox flag is more accurately called a carrier signal flag.

As the term suggests, the carrier signal flag serves as a signal to your postal carrier that there is mail in your mailbox that you want to have picked up and delivered elsewhere.

This is called outgoing mail, and raising the carrier signal flag will allow the postal carrier to stop by your mailbox even if they have no mail to drop off.

Previously, and particularly in the rural parts of America, they also used the carrier signal flag for incoming mail. Because some mailboxes were some distance from the homes in the countryside, the postal service workers would raise the carrier signal flag to alert the homeowner of new mail.

If the homeowners did not see the flag up, they would save themselves from what would otherwise turn out to be a long trip in vain.

The United States mailbox system is different from the Royal Mail in the United Kingdom. The Royal Mail does not offer the service of collecting mail from private homes for posting.

That means you won’t see any mailbox in the UK with a flag up at any time. All the residential mailboxes are simply for receiving incoming mail.

Do All Mailboxes Need Flags?

Not all mailboxes have carrier signal flags.

It is entirely up to the resident or homeowner if they wish to use their curbside mailbox for outgoing mail.

Some persons choose to use their mailbox for incoming mail only, in which case they will not need a flag. The United States Postal Service (USPS) calls this its Limited Service.

However, once the purpose of your mailbox is to send out mail as well, the USPS requires that you put a carrier signal flag in place. This flag must be raised when there is outgoing mail to have it picked up by the postal carrier.

This kind of service is put in the category of the “USPS Full Service.”

However, there are cases when outgoing mail does not need a carrier signal flag at all. This is what happens when residents use a centralized mail delivery system. There is a one-way slot for outgoing mail into which residents deposit their mail in these cases.

Postal service workers will then access the outgoing mail by using a key.

What Kind of Flags CAN Mailboxes Have?

The color of your carrier signal flag must be in clear contrast to the main color of your mailbox. The United States Postal Service prefers a fluorescent orange color for the carrier signal flag.

There are also restrictions on the material you can use for your carrier signal flag. According to the USPS Engineering Standards Specifications, the material of choice is plastic.

This is logical since plastic will not shatter or corrode due to its exposure to the elements. Plastic is also a good choice because it is light enough to meet two pounds or less mailbox flag weight requirement.

The position of the carrier signal flag on the mailbox is also standardized. It needs to be on the right side when viewing the mailbox from the front. It must also be of a design that allows it to stay in place until the postal worker retracts it.

The carrier signal flag needs at least 4 square inches of the exposed surface when it is engaged for visibility. For safety, the mailbox flag must be free from sharp edges.

Self-lowering flags are permitted if they meet the following requirements:

  • They must not need any extra effort from the mail carrier
  • They must not have any part sticking out to interfere with the mail carrier’s duties
  • They must not pose any hazard to the mail carrier

What Kind of Flags CAN’T Mailboxes Have?

The USPS forbids only five colors on the carrier signal flags.

They are white, green, blue, yellow, and brown. These colors are not approved for carrier signal flags because they are not easily visible and might be missed by a passing postal carrier.

The USPS Engineering Standards Specifications also clearly prohibit wood from being used as a material. This is probably because wood can splinter and break as it sits out in the open.

Wood is also more dense than plastic, so it will require more than two pounds of force to be retracted. The USPS does not permit the use of more than two pounds of force to raise a carrier signal flag.

When Are Flags Required on Mailboxes?

Carrier signal flags are only required on full-service mailboxes.

Full-service mailboxes are meant to allow for both incoming and outgoing mail. They are the most popular choice of homeowners because they spare homeowners the trip to a post office for posting mail.

Limited service mailboxes are only for receiving mail, so they do not require any special alert to the postal carrier. That’s why mailbox flags are only required for full-service mailboxes.

They are also not required to use a centralized mail delivery system. The USPS offers curbside mailboxes for single-unit residences. But they also provide centralized mail delivery for communities. 

A centralized mail delivery system is a collection of multiple mailbox units in a single and central area. It’s a cheaper option for the USPS, and it supports a sense of community and socialization within a neighborhood.

One type is called a CBU, or Cluster Box Unit, which typically is free-standing and mounted on a pedestal. Another type is directly mounted to a wall called the 4B mailbox.

The 4C mailbox is also wall-mounted but is now the standard for central delivery systems because it comes with bigger compartments and offers better security.


USPS Engineering Standards Specifications

5 Myths About Carrier Signal Flags in Mailboxes

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