A Commercial Mailing Receiving Agency (CMRA) is a private company—such as The UPS Store (formally Mailboxes Etc.) or FedEx Kinkos—that provides mailbox rental services to individuals and companies.
Any address processed using SmartyStreets is closely inspected. If it is found to correspond to a CMRA, we flag it so that you can handle the address according to the needs of your business. See field definitions for details.
Being able to properly identify CMRA-based customers has many advantages, including fraud prevention and arranging delivery. If you need to know where somebody lives, a CMRA box won't help you. If you know that you have the address of a CMRA mailbox, you can request the information you need and make other inferences.
More information at the official USPS site.