Secure Implementation Method of POP before SMTP Using a Relay Server with SSL Protocol

概要

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POP before SMTP is a method for controlling access to SMTP servers. In this method, a user is required to be authenticated in a POP session before starting SMTP sessions. This method is very popular since the system is constructed on these basic protocols, however, when a POP server is located in DMZ, the server which might contain secret information such as mails has risk of being attacked by malicious users. On the other hand, an SMTP server should be located in DMZ, since an SMTP server is expected to have heavy traffic with other sites. In order to protect a POP server from attacks by means of a firewall, we introduce a new implementation method of POP before SMTP. In this implementation, a relay server which relays messages in a POP session to the POP server is located inside of the firewall. With the construction, the relay server monitors a POP session and notifies the result of the session to the SMTP server which is located in DMZ as in the case of usual setting. In addition, we improved security of the system by executing a POP session over an SSL channel.
2003-04-01