No, I don't think you will pay a penalty, but hold on to the original envelope. It's your proof that you mailed it on time.
Follow this link and check the address on the right for that correct mailing address.
If you owe some tax with your return, and you get a letter assessing a penalty, please contact the Audit Support Center here. They can help you with your letter and a claim for reimbursement if the penalty isn't waived.