How can one prove a tax return was filed if the IRS says it was not?

Was the return sent by certified mail, return receipt requested? If so the green card signed by someone at the IRS and a copy of thee signed and dated tax return is all the proof needed.  If you did not send it certified, check with your tax preparer.  He or she should have some sort of proof of filing.  If you filed electronically, as most do, you should have a confirmation statement that will serve as proof.  If all else fails, send a copy of your signed and dated return along with a short affidavit that you sent it on that day to the IRS.  As we approach the new filing deadline of July 15 for filing returns and other tax documents, please remember, anytime you mail something to the IRS always send it certified and never send any original documents (except for tax returns), just send copies. Also, always keep a signed and dated copy of your tax return.