Abstract: In accordance with the present invention a multiple use envelope for safely sending material to successive recipients is provided. The envelope broadly is a paperboard container having a generally rectangular, substantially closed body with one open edge opening into an interior cavity for receiving material. A closure flap is connected to the body adjacent the open edge and can be manipulated to close the opening. On its interior surface, the closure flap carries two parallel sealing strips and two parallel opening strips for use by first and second senders and recipients. On its exterior surface, the closure flap carries an indicia receiving security block overlying at least a portion of at least one of the two opening strips. The invention also encompasses a flat paperboard blank for forming into the envelope.