A system for controlling friction forces acting on a mailpiece in a mailpiece insertion module. The system includes at least one friction drive belt, a repositionable backstop assembly for arresting the motion of the envelope when disposed in a first position and permitting the conveyance along the feed path when disposed in a second position, an actuator operative to position the backstop assembly into the first and second positions and consuming energy to maintain the backstop assembly in the first position, a sensor for measuring the magnitude of energy consumed by the actuator; a means for developing a pressure differential across the envelope to urge the envelope into frictional engagement with the drive belts and for developing friction forces along a mating interface between the envelope and the friction drive surface, and a system controller, responsive to a sensed signal indicative of the energy consumed, for varying the magnitude of the pressure differential and the friction forces developed along the mating interface of the envelope.