Bulk Mailing vs. Single Piece Mailing

Bulk mail or bulk mailing, also known as commercial mail and marketing mail, is a classification of mailings through the USPS which allows for discounted rates on postage based upon compliance with USPS guidelines that include the following:

• Obtain a mailing permit from the USPS for the class of mail you wish to utilize including payment of annual fees. Examples of classes of mail are first class, periodical, nonprofit.
• Ensure your mailing list addresses are accurate by running a NCOA and/or CASS certification on the list. For more information see mailing services.
• Presort your mail pieces by zip code. If you are using a mailing service provider or printer with in-house mailing capabilities, this will most likely be part of that service.
• To qualify for a bulk mailing or commercial business mailing you must have a minimum of 200 pieces or a minimum of 50 lbs. of mail. For First-class presorted, you must have 500 pieces.
• Extra attention must be given to the size and shape of your mailpiece as it must fit within size and aspect ratio requirements for bulk mailing.

In contrast, single-piece mail refers to the kind of mail you send one piece at a time or in very small quantities. This could be your personal correspondence such as bills, birthday cards, etc. When you put a postage stamp on an envelope, that is full price postage for a single piece.

Source: usps.com