The revitalization of e-business via Internet brings big changes to the postal business, and leads to a tremendous increase of heavy and large sized postal mails with continuing growth of home delivery business. Thus, even though the number of intermediate storages for mail delivery that mailmen use for picking up mails in the middle of mail delivery has been being increased, it has still many problems such as insufficient number and size of the storages as well as avoidance of mail keeping of trust agents. It is necessary that safety of mail keeping, seamless mail delivery, and individual parcel pick-up process reestablishment should be made through an improved counter plan for the problems described previously. This study presents the efficient and right operational plan for the intermediate storage for mail delivery with providing the number and size of intermediate storages per mail delivery sequence according to four different types of post offices.