Bulk mail broadly refers to mail that is mailed and processed in bulk at reduced rates. The term does not denote any particular purpose for the mail; in particular, it is not synonymous with "junk mail."
As an example, in the United States, the United States Postal Service (USPS) defines bulk mail broadly as "quantities of mail prepared for mailing at reduced postage rates." The preparation includes presorting and placing into containers by ZIP code. The containers, along with a manifest, are taken to an area in a post office called a bulk mail entry unit. The presorting and the use of containers allow highly automated processing of the mail, both in bulk and piecewise, in processing facilities called bulk mail centers (BMCs).
In 2009, the USPS announced plans to streamline sorting and delivery, which would recast the BMCs as "Network Distribution Centers
Although bulk mail, junk mail and admail are, strictly speaking, not synonymous, the terms are used in common parlance to refer to unsolicited invitations delivered by mail (typically, but not invariably, at bulk rates) to homes and businesses.
Advertising mail includes advertising circulars, catalogs, CDs, “pre-approved” credit card applications, and other commercial merchandising materials delivered to both homes and businesses.