In an e-mail receiving apparatus, a user management table arranged to include each combination of a user ID that is used for identifying a plurality of users and a unique ID that is newly set each time a new user is registered in an S/MIME gateway apparatus. A received e-mail management table is arranged to include a plurality of records each indicating an association relation between each e-mail received from an e-mail server apparatus, and the user ID and the unique ID of a destination user of the corresponding e-mail. A main control unit is arranged to read out each record of the received e-mail management table, determine whether or not the unique ID related to the read-out record is in the user management table, and delete the read-out record from the received e-mail management table when the unique ID is not in the user management table. Accordingly, a system is provided in which, when a registration of a user of a distribution destination is deleted, received e-mails are properly processed.