Yes, you can use USPS to mail your tax documents to the IRS. The IRS recommends using USPS certified mail, return receipt requested, to mail your tax documents. This service provides proof of mailing and delivery, and allows you to track your documents to ensure they reach the IRS safely. To use this service, simply take your tax documents to your local post office and request certified mail, return receipt requested. The post office will provide you with the necessary paperwork and a certified mail receipt, which you should keep for your records. The IRS also accepts tax documents submitted electronically using e-file. This is often the fastest and most convenient way to submit your tax documents. You can find more information about e-file on the IRS website.