The term "bulk mail" refers to larger quantities of mail prepared for mailing at reduced postage rates. In business, the term "bulk mail" means discounted First-Class Mail and advertising mail (called "Standard Mail" by the Postal Service). Discounted rates are available for other classes of mail, too. The Postal Service uses the terms "bulk" and "presorted" interchangeably.
Bulk rates are discounted from "single-piece" rates. "Single-piece" means that you pay the full postage rate; when you put a 42-cent stamp on a letter, you're paying the single-piece rate. Many mailers pay single-piece rates even though they are doing large mailings. Why? Because they don’t want to do any extra preparation work—they don’t have the time, or it’s just not cost effective for their business. Business Mail 101 will help you make smart choices about your own mail to determine if bulk rates are right for you.
The Postal Service offers discounts for bulk mailings because you do some of the work that otherwise would have to be done by the Postal Service (for example, sorting the mail by ZIP Code or transporting the mail to a different postal facility). Everyone benefits from this "worksharing." Mailers make an investment in time and technology, and the Postal Service’s costs are reduced and you pay less postage.
Direct marketing is the use of postal mail sent in bulk for the purposes of marketing, advertising, or promotion. It is used by businesses, non-profit organizations, and political candidates alike.
Typically, direct mail sent in bulk is mailed at a discounted postal rate from individual letters, with a special bulk mailing rate available by obtaining a bulk mail permit from the post office.
Opting out of junk mail
Direct mailers use mailing lists of likely prospects which they buy or rent from bulk mailing list brokers, and in turn trade or sell the names and addresses of their customers with these mailing list brokers and with other business and organizations. Many people do not like to receive bulk mail they did not ask for, so in the United States the Direct Marketing Association maintains an opt-out list . This list is only partially effective as many direct mailers are not members of the Direct Marketing Association. Another technique to curtail the amount of bulk mail one receives is asking every business and organization with which one does business through the mail to not sell or trade your name and address with any other company.
A detailed and well-written guide is here.
Political direct mail
Direct mail has become a common fundraising and organizing method for political groups. The use of direct mail for political organizing was pioneered by conservative activist, Richard Viguerie starting in 1965.