Chapter 33 Anti-Spam

Figure 427 Anti-X > Anti-Spam > DNSBL

The following table describes the labels in this screen.

Table 182 Anti-X > Anti-Spam > DNSBL

LABEL

DESCRIPTION

Enable DNS Black

Select this to have the ZyWALL check the sender and relay IP addresses in e-

List (DNSBL)

mail headers against the DNSBL servers maintained by the DNSBL domains

Checking

listed in the ZyWALL. The ZyWALL checks public IP addresses (it does not

 

check private IP addresses).

 

The ZyWALL queries all of the DNSBL domains at the same time.

 

If any of the e-mail header’s IP addresses match an entry in a blacklist on one of

 

the DNSBL domains, the ZyWALL immediately classifies the e-mail as spam

 

and takes the action specified in the anti-spam policy. The ZyWALL does not

 

wait for replies from other DNSBL domains.

 

If none of the e-mail header’s IP addresses are on any of the DNSBL domains,

 

the ZyWALL classifies the mail as valid and forwards it.

 

The ZyWALL records DNSBL responses for IP addresses in the cache for up to

 

72 hours. The ZyWALL checks an e-mail header’s IP addresses against the

 

cache first and only sends DNSBL queries for IP addresses that are not in the

 

cache.

 

 

DNSBL Spam Tag

Enter a message or label (up to 15 ASCII characters) to add to the beginning of

 

the mail subject of e-mails that have a sender or relay IP address in the header

 

that matches a blacklist maintained by one of the DNSBL domains listed in the

 

ZyWALL.

 

This tag is only added if the anti-spam policy is configured to forward spam mail

 

with a spam tag.

 

 

Max. IPs Checking

Set up to how many sender and relay server IP addresses in the mail header to

Per Mail

check against the DNSBL.

 

 

IP Selection Per

Select first N IPs to have the ZyWALL start checking from the first IP address in

Mail

the mail header. This is the IP of the sender or the first server that forwarded the

 

mail.

 

Select last N IPs to have the ZyWALL start checking from the last IP address in

 

the mail header. This is the IP of the last server that forwarded the mail.

 

 

Actions when Query

Use this section to set what the ZyWALL does if the queries to the DNSBL

Timeout

domains time out.

 

 

 

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ZyWALL USG 100/200 Series User’s Guide