To begin, a folded mailer is defined as a single piece of paper or several pieces of paper that have been folded together, bound or not, to be sent without an outer covering or envelope to contain it. Even if the design of your folded mailer allows it to fit the size or shape of another mail piece, like a post card, after the piece is folded it is considered a folded mailer.
In folding your mailer, there are different designs which are compatible with machine processing and U. S. Post Office requirements. Folding your mailer correctly will greatly improve the processing and delivery service for your mailing. In deciding how to fold your mailer the two important distinctions to make are first, between open edges and folded edges, and second, between leading edges and trailing edges. As a rule, mailers should be folded so the leading edge is also a folded edge, and the trailing edge should be the open edge.
Open edges and folded edges are easy to see; the open edge(s) of the mailer and the folded edge(s). The leading and trailing edges are also easy to understand. Leading edges are the first to go through a mail processing or sorting machine, while the trailing edge is the last.
Here is an illustration to help show the leading and trailing edges:
So, the leading edges should be folded edges and the trailing edges should be open edges:
But what if your mailer has more than one folded edge? Let's look at what is commonly known as a tri-folded mailer. A sheet of normal office or copy paper, folded into thirds as if it were a letter to be placed into an envelope, has two folds and one opening. In this case, the mailer should open at the top rather than the bottom, as shown below, with the addressing and postage pictured to show how the mailer is oriented.
This picture shows how you would properly orient the addressing and postage for a folded mailer like this(known as a quad fold).
The final fold is along the bottom edge of the mailer. The right edge of the mailer is also a folded edge, but the bottom edge would be the final fold. While neither of the open edges would be thought of as "final," these examples help illustrate how any mailer should be folded in order to have folded edges and final folded edges in the correct place.
Each style of folded mailer must have the open edge secured in order to be mailable. The best way to do this is by using self-adhesive white tabs folded around the final opening. For example, if you were to use a folded mailer that required two tabs along the top of the mailer, the tabs would be placed as shown below. Using either staples or tape to secure the open edge of the mailer is not recommended. Either staples or scotch tape may damage the postage or sorting machines used to deliver your mail.
In this example, the top edge of the mailer is open and the tabs(which are circular when laid flat) have been folded around the open edge, half on the front and half on the back. This secures the opening and allows for machine processing.