I have had several clients have their estimated tax payment 1040es returned by the Post Office with the message address unknown. I have verified that the address on the envelope is the same as that on the payment voucher.
Has this happened to anyone else?
IRS changed a bunch of addresses this year, I know the ES payment address for CA is across the country from where we've sent them for at least the last decade.
Have you checked the IRS website to see if the program is printing the wrong address or not?