Zyxel ZyWALL 1100 [547/829] A b c d not spam

Zyxel USG 60 [547/829] A b c d not spam
Chapter 32 Anti-Spam
ZyWALL/USG Series User’s Guide
547
Figure 360 Conflicting DNSBL Replies Example
1 The ZyWALL/USG receives an e-mail that was sent from IP address a.b.c.d and relayed by an e-
mail server at IP address w.x.y.z. The ZyWALL/USG sends a separate query to each of its DNSBL
domains for IP address a.b.c.d. The ZyWALL/USG sends another separate query to each of its
DNSBL domains for IP address w.x.y.z.
2 DNSBL A replies that IP address a.b.c.d does not match any entries in its list (not spam).
3 While waiting for a DNSBL reply about IP address w.x.y.z, the ZyWALL/USG receives a reply from
DNSBL B saying IP address a.b.c.d is in its list.
4 The ZyWALL/USG immediately classifies the e-mail as spam and takes the action for spam that you
defined in the anti-spam policy. In this example it was an SMTP mail and the defined action was to
drop the mail. The ZyWALL/USG does not wait for any more DNSBL replies.
DNSBL A
DNSBL B
DNSBL C
IPs: a.b.c.d
w.x.y.z
1
2
a
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b
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c
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d
N
o
t
s
p
a
m
3
4
a
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b
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c
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d
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w
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x
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y
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z
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a
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b
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c
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d
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w
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x
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y
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a.b.c.d?
w.x.y.z?
a.b.c.d Spam!

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