Cisco Cisco Email Security Appliance C170 Guia Do Utilizador

In order to classify connections to the appliance and apply mail flow policies (which may or may not 
contain rate limiting), a listener's Host Access Table (HAT) uses the following methodology: 

 

For more information, refer to “Sender Groups Defined by Network Owners, Domains, and IP 
Addresses” in the “Configuring the Gateway to Receive Email” chapter of the Cisco IronPort AsyncOS 
for Email Configuration Guide. 

The “Classification” stage uses the sending host’s IP address to classify an inbound SMTP session 
(received on a public listener) into a Sender Group. The Mail Flow Policy associated with that Sender 
Group may have parameters for rate limiting enabled. (Rate limiting limits the maximum number of 
messages per session, the maximum number of recipients per message, the maximum message size, 
and/or the maximum number of concurrent connections you are willing to accept from a remote host.)

Normally, in this process, recipients are counted against each sender in the corresponding named sender 
group. If mail is received from several senders in the same hour, the total recipients for all senders is 
compared against the limit.

There are some exceptions to this counting methodology:

If the classification is done by Network Owner, then the SenderBase Information Service will 
automatically divide a large block of addresses into smaller blocks. 

Counting of recipients and recipient rate limiting is done separately for each of these smaller blocks 
(usually, but not always, the equivalent of a /24 CIDR block). 

If the HAT Significant Bits feature is used. In this case, a large block of addresses may be divided into 
smaller blocks by applying the significant bits parameter associated with the policy. 

Maximum Recipients per 
Hour 

max_rcpts_per_hour

Number

5k

Maximum Recipients per 
Hour Error Code

max_rcpts_per_hour_code

Number

452

Maximum Recipients per 
Hour Text (*)

max_rcpts_per_hour_text

String

Too many

 

recipients

Use SenderBase

use_sb

on | off

on

Define SenderBase 
Reputation Score

sbrs[value1:value2]

-10.0- 10.0

sbrs[-10:-7.5]

Directory Harvest Attack 
Prevention: Maximum 
Invalid Recipients Per 
Hour

dhap_limit

Number

150