Mailbox Flag – Meaning & How It Works?

We come across different mailboxes daily, some with mailbox flags and others without. But many people don’t know the meaning of a mailbox flag or its purpose.

Basically, a mailbox flag is an indicator used by the owner to notify the USPS courier of outgoing mail. It can be placed in two different ways, each having a specific meaning to the courier.

In this article, I will discuss the mailbox flag, the purpose of a mailbox flag, and the USPS design and color requirements for a mailbox flag for those looking to get one.


Not all traditional mailboxes have the mailbox flag because their main purpose is to receive mail. Over time, having the option to notify the postal courier of outgoing mail made more sense to people.

Most people now choose to have the mailbox flag installed to get more out of their mailboxes. A mailbox flag, also known as a courier signal flag, is an indicator for the postal courier.

It is usually attached to the right-hand side of the box, that is the right side from the front end. It may be of any color, aside from white, green, yellow, brown, or blue.

Mailbox flag indicators

There are two main indicators a mailbox flag gives, each of which has a different meaning to the postal courier. The two indicators are:

1. No outgoing mail

mailbox flag down - threaller

The first indicator is said to be no outgoing mail. This indication is sent when the mailbox flag is set in a horizontal position.

When the postal courier sees this, he simply understands that the customer has no outgoing mail. If the courier has any incoming mail for the customer, he or she places it in the box and gets on with his or her delivery.

2. Available outgoing mail

mailbox flag up - threaller

The second indicator indicates that there is available mail for delivery to another destination. This signal is sent when the mailbox flag is placed in a vertical position, that is when the flag is facing up.

When the poster courier sees this indicator, he/she knows that the customer has outgoing mail. He or she proceeds to get the mail that is to be delivered.

USPS mailbox flag requirements

Different types of mailboxes are available on the market for people to purchase. However, the USPS has some requirements for mailbox flags.

Some of the major ones are;

  • The mailbox flag position: Must be situated at the right-hand side of the box, that is from the front view of the mailbox.
  • The mailbox flag design: The mailbox flag must not be too firm or light. It can’t require more than two pounds of force to be moved and must not be too light, so it doesn’t move on its own.
  • The mailbox flag color: The preferred color is fluorescent orange, but the customer can still have other colors. However, there are some colors that they don’t accept. They are; any shade of white, green, yellow, brown, or blue.

Additionally, the color of the mailbox flag must be different from the mailbox itself. You can see a complete guide of the USPS mailbox flag requirement for more guidance here.


Can you put a mailbox flag on your mailbox?

Yes, you can. You can purchase a mailbox flag on Walmart and manually install it on your mailbox.

Where does the flag go in the mailbox?

The flag has to be placed on the right end of the mailbox. That is the right end when facing the front of the mailbox.

How much do mailbox flags cost?

A mailbox flag costs between $5 – $15.


A mailbox flag is an indicator placed on the right-hand side of the mailbox. The mailbox flag can be placed in one of two ways with each sending a particular message to the postal courier.

Its main purpose is simply to notify whether a customer has any outgoing mail to send. If it is placed vertically, it indicates there is, and if placed horizontally, it means there is no outgoing mail.

In addition to your mailbox, you might also find the USPS informed delivery feature helpful. See this article on informed delivery and how you can sign up for this service.

I hope you enjoyed reading this article. Thanks for reading.