If you're e-filing your extension through TurboTax Easy Extension, you don't need to mail anything, unless you're paying additional taxes owed by check.
Both Easy Extension and the TurboTax software will provide the correct mailing address if you're paper-filing Form 4868 and/or sending in check payment.
You can also obtain this information from the IRS Form 4868 instructions (at the top of page 4). The exact mailing address is determined by where you live and whether you're including payment with your extension.
