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Chapter 33 Anti-Spam
ZyWALL USG 100/200 Series User’s Guide
569
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
List (DNSBL)
Checking
Select this to have the ZyWALL check the sender and relay IP addresses in e-
mail headers against the DNSBL servers maintained by the DNSBL domains
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
Per Mail
Set up to how many sender and relay server IP addresses in the mail header to
check against the DNSBL.
IP Selection Per
Mail
Select first N IPs to have the ZyWALL start checking from the first IP address in
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
Timeout
Use this section to set what the ZyWALL does if the queries to the DNSBL
domains time out.