Abstract: A foliaceous pre-cut blank has a rectangular back part and, joined thereto, at least one side flap, a bottom flap and a closing flap. A first fold line is located at the transition from the back part to the closing flap. The closing flap is divided into first and second sections by a second fold line running in parallel to the first fold line, the first section being located between the first and second fold lines. The blank is conveniently assembled into an envelope. A first adhesive strip seals the envelope for a first mailing, and a second adhesive strip can be used to seal the envelope for a return mailing.