The IRS has proposed amending the U.S. Treasury Department rules that said a registered or certified mail receipt is the only legitimate evidence of having met the IRS’ tax filing deadline.

“The proposed regulations affect taxpayers who mail federal tax documents to the IRS or the U.S. Tax Court,” the IRS said.

Specifically, the IRS said use of a primary delivery service also may serve as legitimate proof of satisfying the delivery rule, which had been limited to use of certified or registered mail.

When published as a final regulation, the amended rule will apply to all documents mailed after Sept. 21 this year.