Question
If I electronically file the taxpayer's extension, can the taxpayer send a payment by mail?
Answer
Yes. If the taxpayer wants to pay by check or money order, they can do so even if the extension was filed electronically. Per Form 4868 instructions, "If you e-file Form 4868 and mail a check or money order to the IRS for payment, use a completed paper Form 4868 as a voucher."
Related topic: 1040-US ELF: Electronic filing FAQs