The invention relates to an apparatus and a method for automatically closing envelopes. The apparatus contains a transport means for moving the envelopes in a transport direction, and a means for automatically folding back and closing an envelope flap. To enable accurate and reliable closing even of tightly filled envelopes even in a continuous operation duty, the means for automatically folding back and closing the envelope flap comprises several rotors which are rotatable in the transport direction of the envelopes and are movable, by means of a drive, in a manner which is transverse to the transport direction of the envelopes.