A feeder (12) for feeding envelopes in a mail handling machine comprising a transport deck (30) for receiving a stack of envelopes, feed rollers (34) for conveying downstream envelopes towards a reference wall (32) leaving a clearance path for the envelopes; a stack sensor (48) for detecting the presence of the stack of envelopes at a predetermined height threshold; and a control unit (46) configured for decreasing acceleration of the feed rollers when the stack of envelopes goes below the predetermined height threshold.