The organization of the mail concentration lays on the simultaneous and interdependent definition 1) of the sorting work made in post—offices and their sorting center and 2) of the multiple vehicules routing problems with time windows that vary with the sorting level in post offices. A scenario approach is used to focus only on the afternoon mail picking, that is to perform during a very short period. Then the vehicule routings may be qualified as <wire-routings>, instead of <loop-routings>. A model using linear programming is given and used to solve an actual problem (with GAMS). Then, a model generalization is done for including the possibility of including some <pre-sorting centers> between post—offices and the sorting center (network design) and of defining the optimal vehicules float.