A feeder device for feeding mailpieces to a postal sorting conveyor has an unstacker head designed to put the mailpieces in series and on edge on the sorting conveyor, an unstacker plate designed to unstack the mailpieces one-by-one towards the unstacker head, and a mailpiece feed conveyor designed to convey the mailpieces in a stack and on edge against the unstacker plate. The unstacker plate has a stationary portion that extends from the unstacker head, and a moving portion that extends the stationary portion, said moving portion being mounted to pivot from the stationary portion between a first position in which the stationary portion and the moving portion are aligned with each other, and a second position in which the stationary portion and the moving portion are angularly offset relative to each other.