Smtp Alg Usage - D-Link NetDefendOS User Manual

The SMTP ALG can be used to process both SMTP traffic between mail servers as well as from
clients to servers. A typical mail sending sequence would be the following:
1. A local user sends an email to a mail server. This might be sent using SMTP or Microsoft
Activesync™ or some other protocol.
2. The local mail server performs a DNS lookup of the destination domain name to determine
the IP address of the remote mail server to forward the mail to.
3. The email is forwarded to the remote server using SMTP.
4. The remote user retrieves the email from the remote mail server using POP3 or IMAP or
Activesync or some other protocol.
SMTP ALG Setup
To set up security using the SMTP ALG, perform the following steps:
• Create a new SMTP ALG object with the desired options enabled, such as file blocking and
virus scanning.
• Create a new custom Service object for SMTP with the following properties:
i. Type: TCP
ii. Destination: 25
iii. Enable Syn Flood Protection if traffic is coming from the Internet. Having this disabled
will use less NetDefendOS resources but disable it only where a denial-of-service attack
is unlikely.
This is now a copy of the predefined Service object called smtp-in. If Syn Flood Protection is
Figure 6.4. SMTP ALG Usage
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Chapter 6: Security Mechanisms