An envelope closing mechanism with a deflector (11; 61) for urging a flap (6) of an envelope (3) from the transport path (20; 70); and a moistener (7) for moistening at least a portion of the flap (6) of an envelope (3). The deflector (11; 61) is movable between a position of rest on a side of the transport path (20; 70) located opposite the moistener, and a deflecting position on the other side of the transport path (20; 70) for urging the flap (6) of the envelope (3) against the moistener (7). If the deflector (11, 61) is in the deflecting position, it releases the transport path (20; 70) for transporting the envelope (3) along the deflector (11, 61). From a position in which the flap (6) of the envelope (3) extends between the moistener (7) and the deflector (11) in a deflecting position, the envelope (3), following the transport path (20; 70) is transported along the deflector (11) in the deflecting position with the fold leading. A method for closing envelopes is also described.