My extension says it is accepted. Do I have to mail the form also?

Which form are you asking about mailing?

Form 4868.  

You do not need to also mail this form into the IRS.  Since it was submitted electronically and accepted, you have successfully filed your extension

Hi-

You should not need to mail in any forms.  However, please remember to submit payment for any balance due that you may owe prior to midnight tonight.  Otherwise, interest can be applied to your balance due when you do file in the extension period