Cisco Cisco Email Security Appliance C170 Guia Do Utilizador

The Header Repeats rule evaluates to 

true

 if at a given point in time, a specified number of messages:

With same subject are detected in the last one hour.

From same envelope sender are detected in the last one hour.

You can use this rule to detect high volume emails. For example, political campaigns through certain 
websites may send out emails to organizations in high volumes. Anti-spam engines treat such emails as 
clean, and do not stop the delivery of these emails.

The syntax of this rule is 

header-repeats (<target>, <threshold> [, <direction>])

, where:

<target>

 is 

subject

 or 

mail-from

. AsyncOS counts the repetition of values of the target.

<threshold>

 is the number of messages with identical values for a given target, received in the last 

one hour, beyond which the rule evaluates to true.

<direction>

 is 

incoming

, 

outgoing

, or both. If direction is not specified in this rule, incoming or 

outgoing messages are counted for rule evaluation.

Every time when a Header Repeats rule evaluates to 

true

, a System Alert is sent. See 

If the header field includes comma or semi-colon separated values, the rule considers the complete string 
for tracking. This rule ignores messages with empty subject header.

The Header Repeats rule maintains a moving sum of messages with up to one minute’s precision. As a 
result, after the set threshold has reached, there can be a delay of one minute before this rule is triggered.

You can use the Header Repeats rule with other rules using AND or OR operators. For example, you can 
whitelist a subset of messages using the following filter:

When you use a Header Repeats rule with another rule using AND or OR operators, the Header Repeats 
rule is evaluated last, and only if needed. If a Header Repeats rule is not evaluated for a given message, 

subject

 or 

mail-from

 is not counted to compare with the supplied threshold.

As Header Repeats rule is evaluated last and only if needed, the behavior of this rule may vary when 
used with other rules using an OR operator. The following sample filter uses an OR condition of Signed 
and Header Repeats rule.

F1: if (recv_listener == 'Gray')  AND (header-repeats('subject', X, 'incoming') { 

drop();}

f1: if signed OR (header-repeats('subject', 10)) { drop();}