Machine for sewing envelopes into pouches, in correspondence with an opening delimited by two free overlapping flaps, the machine includes a support base; a sewing head, mechanically mounted on the support base, configured to make a sewing line along a sewing direction; retaining means for retaining the free flaps of said envelope like a bag; first movement means for realizing a relative movement between said sewing head and the holding means along a first movement direction substantially parallel to the sewing line; second movement means for moving the sewing head and/or holding means at least along a second movement direction orthogonal with respect to the first movement direction; at least a first sensor configured to detect an extremal edge of the free edges; at least one electronic control unit for generating the relative motion between the support base and/or the holding means along the second movement direction.