When you set up a scheduled direct debit it will go through you would not need to mail the payment. During non-peak times, funds are usually withdrawn on the payment date you specify, assuming your e-filed return has already been accepted (received) by the IRS.
Due to high e-filing volume it can take a little longer to process the payment and then it will take your bank another few days to post the debit to your account.
No worries; as long as you selected April 18, 2017 (or earlier) as your payment date, you won't get penalized for a late payment.
If it has been more than 10 days since your Federal tax return was accepted and you don't see the debit you can contact IRS e-file Payment Services at 1-888-353-4537 for assistance in confirming the scheduled debit date.
