D-Link NetDefendOS User Manual page 456

• Name: smtp_inbound_sat
• Action: SAT
• Service: smtp_inbound_service
• Source Interface: wan
• Source Network: all-nets
• Destination Interface: core
• Destination Network: wan_ip
• SAT Translate: Destination IP
• New IP Address: mail_server_ip
3. Click OK
ii. Create a matching ALLOW IP rule to permit the translated traffic:
1. Go to: Policies > Firewalling > Main IP Rules > Add > IP Rule
2. Now enter:
• Name: smtp_inbound_allow
• Action: Allow
• Service: smtp_inbound_service
• Source Interface: wan
• Source Network: all-nets
• Destination Interface: core
• Destination Network: wan_ip
3. Click OK
6.2.6.1. ZoneDefense with the SMTP ALG
ZoneDefense is a feature that allows NetDefendOS to block hosts and networks by sending
management commands to certain types of external network switches. SMTP is used for both
mail clients that want to send emails as well as mail servers that relay emails to other mail
servers. When using ZoneDefense together with the SMTP ALG, the only scenario of interest is to
block local clients that try to spread viruses in outgoing emails.
Using ZoneDefense for blocking relayed emails to an incoming SMTP server would be
inadvisable since it would disallow all incoming emails from the blocked email server. For
example, if a remote user is sending an infected email using a well-known free email company,
blocking the sending server using ZoneDefense would block all future emails from that same
company to any local receiver. Using ZoneDefense together with the SMTP ALG should therefore
be used principally for blocking local email clients.
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Chapter 6: Security Mechanisms