ZyXEL Communications USG110, Руководство пользователя

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Chapter 40 Anti-Spam
ZyWALL USG Series User’s Guide
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40.8 Anti-Spam Technical Reference
Here is more detailed anti-spam information.
DNSBL
• The Zyxel Device checks only public sender and relay IP addresses, it does not check private IP
addresses.
• The Zyxel Device sends a separate query (DNS lookup) for each sender or relay IP address in the e-
mail’s header to each of the Zyxel Device’s DNSBL domains at the same time.
• The DNSBL servers send replies as to whether or not each IP address matches an entry in their list. Each
IP address has a separate reply.
• As long as the replies are indicating the IP addresses do not match entries on the DNSBL lists, the Zyxel
Device waits until it receives at least one reply for each IP address.
• If the Zyxel Device receives a DNSBL reply that one of the IP addresses is in the DNSBL list, the Zyxel
Device immediately classifies the e-mail as spam and takes the anti-spam policy’s configured action
for spam. The Zyxel Device does not wait for any more DNSBL replies.
• If the Zyxel Device receives at least one non-spam reply for each of an e-mail’s routing IP addresses,
the Zyxel Device immediately classifies the e-mail as legitimate and forwards it.
• Any further DNSBL replies that come after the Zyxel Device classifies an e-mail as spam or legitimate
have no effect.
• The Zyxel Device records DNSBL responses for IP addresses in a cache for up to 72 hours. The Zyxel
Device checks an e-mail’s sender and relay IP addresses against the cache first and only sends DNSBL
queries for IP addresses that are not in the cache.
Here is an example of an e-mail classified as spam based on DNSBL replies.
Status The activate (light bulb) icon is lit when the entry is active and dimmed when the entry is
inactive.
# This is the entry’s index number in the list.
DNSBL Domain This is the name of a domain that maintains DNSBL servers. Enter the domain that is
maintaining a DNSBL.
Apply Click Apply to save your changes back to the Zyxel Device.
Reset Click Reset to return the screen to its last-saved settings.
Table 281 Configuration > UTM Profile > Anti-Spam > DNSBL (continued)
LABEL DESCRIPTION