The Tax Court website indicates that mail sent to the court through the U.S.  Postal Service or through designated private delivery services may have been returned undelivered.  If a document you sent to the Tax Court was returned to you, as the Tax Court website indicates, re-mail or re-send the document to the Court with a copy of the envelope or container (with the postmark or proof of mailing date) in which it was first mailed or sent. In addition, please retain the original.