Toriss is an IIS plug-in that makes the SMTP service immune to Reverse NDR Attacks. Instead of bouncing emails that are sent to invalid users, Toriss will reject the email as soon as the RCPT command is received. A Reverse NDR Attack can fill the mail queue with thousands of undeliverable bounce-backs, slowing down the whole system and making the SMTP service unresponsive. Toriss solves this problem completely.