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. Complete the form and mail it, along with proof of value and evidence of insurance, to the address on the form. Edit, sign, and share postal service file complaint online. No need to install software, just go to DocHub, and sign up instantly and for free. Here are bbb's five steps in our complaint process. Number one go to bbb. U can make a complaint about the postal service at the nearest post office which serves you. Use the USPS website's Email Us form.