New regulations provide that a evidence of a postmark is not sufficient to prove delivery. ( T.D. 9543, 76 Fed. Reg. 52561 (8/23/11), amending Regs. §301.7502-1, by revising paragraphs (b)(2) and (e) and adding paragraphs (c)(3) and (g)(4)).
If a tax return preparer files returns, the preparer should either hand-deliver them to the IRS, use certified mail, or use an alternative described below.
When a preparer sends returns to clients, the preparer must consider not only recommending that the clients send the returns via certified mail but also:
• warn the clients that the failure to use certified mail might invalidate the returns, and
• encourage the clients to contact the preparer for alternative methods if certified mail does not work for the clients.
Private delivery services, such as UPS or FedEx, can also be used, but you should first confirm by looking at Notice 2004-83 , 2004-52 I.R.B. 1030 or any relevant guidance issued after that.
The IRS stated that it will be issuing more guidance on private delivery services.