The Pop3 Alg - D-Link NetDefendOS User Manual

Network security firewall

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To implement blocking, the administrator configures the ZoneDefense network range to include

all local SMTP clients. The SMTP-server itself should be excluded from this range.

When a client tries to send an email infected with a virus, the virus is blocked and ZoneDefense

isolates the host from the rest of the network.

The steps to setting up ZoneDefense with the SMTP ALG are:

Configure the ZoneDefense switches to be used with ZoneDefense by going to the

ZoneDefense section of the Web Interface.

Set up the SMTP ALG to use Anti-Virus scanning in enabled mode.

Choose the ZoneDefense network in the Anti-Virus configuration of the ALG that is to be

affected by ZoneDefense when a virus is detected.

More information about this topic can be found in Chapter 12, ZoneDefense.

6.2.7. The POP3 ALG

POP3 is a mail transfer protocol that is used by an email client running on the recipients to

download emails from a mail server. The principal difference with the IMAP protocol is that the

entire email and any attachments are downloaded to the client before the email can be

examined. The email is then subsequently stored on the client computer and may be deleted

from the mail server.

The diagram below illustrates a typical usage of the NetDefendOS POP3 ALG. A mail server

located on the DMZ network dmz_net receives emails from the public Internet using the SMTP

protocol. A protected client on the lan_net network downloads emails from this server using the

POP3 protocol. The clients initiate the transfer with POP3, sending a request to the mail server for

the download of emails also using POP3.

As the emails traverse the firewall, the NetDefendOS POP3 ALG examines the data and can block

or allow them according to the behavior specified in the ALG configuration object.

Tip: Exclusion can be manually configured

It is possible to manually configure certain hosts and servers to be excluded from being

blocked by adding them to the ZoneDefense Exclude List.

Chapter 6: Security Mechanisms

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