Mail save backup system and backup method

The present invention provides a mail save backup system and a backup method, capable of raising a containing efficiency of mails in the premise of ensuring fault resistance when the mails are saved. A mail server (10) determines an importance degree of the received mail according to a main importance degree decision table (300). Then the mail server (10) determines the number of backup servers (20) for saving the mail according to a backup server management table (100) and the determined importance degree of the mail, and selects the backup server (20) serving as a save destination. The mail server (10) sends the received mail to the selected backup server (20), and the backup server (20) saves the received mail into a memory part (230).