Cisco Cisco Email Security Appliance X1050 Guía Del Usuario
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Cisco IronPort AsyncOS 7.1 for Email Advanced Configuration Guide
OL-22164-02
Chapter 5 Using Message Filters to Enforce Email Policies
Because the least expensive test is performed first, switching the order of the
items in the test will have no effect. If you want to guarantee the order in which
tests are performed, use nested
items in the test will have no effect. If you want to guarantee the order in which
tests are performed, use nested
if
statements. This is also the best way to ensure
that an expensive test is avoided whenever possible:
expensiveAvoid:
if (<simple tests>)
{ if (<expensive test>)
{ <action> }
}
In a somewhat more complicated example, consider:
if (test1 AND test2 AND test3) { ... }
The system groups the expression from left to right, so this becomes:
if ((test1 AND test2) AND test3) { ... }
This means the first thing the system does is compare the cost of
(test1 AND
test2)
against the cost of
test3
, evaluating the second AND first. If all three tests
have the same cost, then
test3
will be performed first because
(test1 AND
test2)
would be twice as expensive.
Message Filter Rules
Each message filter contains a rule that defines the collection of messages that a
filter can act upon. You define the filter rules, and then you define a filter action
for messages that return
filter can act upon. You define the filter rules, and then you define a filter action
for messages that return
true
.