Envelopes First Day of Issuance and Circulated Letters
Envelopes First Day of Issue
These are envelopes specially designed with the postage stamp "postmarked" with a special stamp prepared to be used "The First Day" of circulation of said stamp. Today the postmark "First Day of Issuance" can still be used for collection purposes, in the philatelic offices of the Argentine Post.
They consist of real letters "actually sent" by mail to some recipient with postage stamps or special stamps.
Letter circulated from Uruguay to Buenos Aires