The extension is automatic and the IRS typically will not respond with an approval letter.
See the following from the instructions:
Use Form 7004 to request an automatic extension of time to file certain business income tax, information, and other returns. The extension will be granted if you complete Form 7004 properly, make a proper estimate of the tax (if applicable), file Form 7004 by the due date of the return for which the extension is requested, and pay any tax that is due.
*A reminder that posts in a forum such as this do not constitute tax advice.
Also keep in mind the date of replies, as tax law changes.
