Presumption of receipt in the regular course of mail

In Gonzalo P. Nava v. Commissioner of Internal Revenue, L-19470, Jan. 30, 1965, the Supreme Court held that, while there is a presumption that a letter duly directed and mailed was received in the regular course of mail, still, there are two facts that must first be proved before the presumption can be availed of: (a) the letter must have been properly addressed with postage prepaid, and (b) the letter must have been mailed.