An automated letter movement system comprising: postal item processing lines adapted to receive incoming postal items; SSM devices configured to receive at input postal items from at least one postal item processing line and adapted to group the postal items forming shingled groups of partially overlapping postal items; a transportation system adapted to move the shingled groups generated by the SSM devices along a feed direction; postal item output processing lines adapted to carry out the sorting of the postal items fed into it; singulator models receiving the shingled groups arriving from said transportation system, each singulator module being configured to only singularize the postal items belonging to a specific group and to send the singularized postal items to a postal item output processing line configured to implement a sorting program for the postal items subjected to singularization.