Direct mail, also known as junk mail, advertising mail or admail, is the delivery of advertising material to recipients of postal mail. It forms a significant subdiscipline of direct marketing. Some organizations attempt to help people opt-out of receiving advertising mail, in many cases motivated by a concern over its negative environmental impact.

Direct mail includes advertising circulars, catalogs, CDs, “pre-approved” credit card applications, and other commercial merchandising materials delivered to both homes and businesses. It may be addressed to pre-selected individuals, or unaddressed and delivered on a neighbourhood-by-neighbourhood basis.

Postal services

Postal systems have enacted lower rates for buyers of bulk mail permits. In order to qualify for these rates, marketers must format and sort the mail in specific ways - which reduces the handling required by the postal service.

Income from advertising mail represents a significant and growing portion of some postal service's budgets, and it is a service actively marketed by them. In Canada, addressed and unaddressed advertising mail accounted for 20% of Canada Post's revenue in 2005, and the share is increasing. Postal services employ the terms advertising mail, admail, and direct mail, while generally avoiding and objecting to the pejorative term junk mail.

In many developed countries, advertising mail represents a significant and growing amount of the total volume of mail. In the United States, direct mail comprised 29% of all mail in 1980 and 43% in 2003.

Design and format

Direct mail permits the marketer to design marketing pieces in many different formats. Indeed, there is an entire subsector of the industry that produces specialized papers, printing, envelopes, and other materials for direct mail marketing. Some of the common formats include:

• Catalogs: Multi-page, bound promotions, usually featuring a selection of products for sale.
• Self-mailers: Pieces usually created from a single sheet that has been printed and folded. For instance, a common practice is to print a page-length advertisement or promotion on one side of a sheet of paper. This is then folded in half or in thirds, with the promotional message to the inside. The two outside surfaces are then used for the address of the recipient and some "teaser" message designed to persuade the customer to open the piece.
• Clear bag packages: Large (often 9x12 or bigger) full-color packages sealed in a clear, plastic outer wrap. The contents show through the clear bag, giving the potential for maximum initial impact. Clear bag packages can be extremely effective and are very affordable based upon the campaign open-rate. Fact: date=December 2007
• Postcards: Simple, two-sided pieces, with a promotional message on one side and the customer's address on the other.
• Envelope mailers: Mailings in which the marketing material is placed inside an envelope. This permits the marketer to include more than one insert. When more than one advertiser is included, this is often called "marriage mail". Valpak is one of the largest examples of a marriage mail service.
• Snap Mailers: Mailers that fold and seal with pressure. The sides detach and the mailer is opened to reveal the message.
• Dimensional Mailers: Mailers that have some dimension to them, like a small box.
• Intelligent Documents: Programmable mail pieces built dynamically from database information, and printed digitally for faster production.