This is the method I use anytime I have to mail documents to the IRS. It takes more time than just sticking a stamp on an envelope and dropping it in the mail, but it accomplishes three things. (1) Provides proof that you mailed something to the IRS. (2) Proves the date the document was mailed. (3) Proves that the IRS received the specific documents you mailed and acknowledged receipt of those specific documents.
