To file a complaint online, select the topic below "What's the reason for your inquiry?" on the USPS "Email us" page. File a complaint against a business with BBB, search for a business to file a complaint against, or find out the status of a complaint you submitted.File an Online Complaint. Postal Inspectors suggest that, before completing a business transaction, contact the Chamber of Commerce, Better Business. Once you complete the online Privacy Act form, you may register a complaint. Her office will submit the Privacy Act form and complaint directly to USPS. To file a complaint, go to the USPS website or call 1–800-ASK-USPS. You may also speak to the manager or postmaster at your local post office. Use our online form to answer a few questions about your issue. Please provide as much detail as you can.