Security system for electronic mail based on digital signature, uses digitally signed certification for transmitting and receiving electronic mails, and limits total certification volume for electronic mails for each user

摘要

The system outputs a digitally signed certification, that includes relevant information for transmission and reception of the electronic mail, for each electronic mail that enters the system with a copy of electronic mail. A similar certification is outputted for the transmitting and receiving addresses without a copy of original electronic mail. The system controls and limits the total certification volume for each user.