Cisco Cisco Email Security Appliance C160 Mode D'Emploi

Use the Import Table button on the Destination Controls page or the 

destconfig -> import

 command 

to import a configuration file.You can also export your Destination Control entries to an INI file using 
the Export Table button on the Destination Controls page or the 

destconfig -> export

 command. 

AsyncOS includes the 

[Default]

 domain control entry in the exported INI file.

You can use the 

destconfig

 command in the CLI to configure Destination Control entries. This 

command is discussed in the CLI Reference Guide for AsyncOS for Cisco Email Security Appliances.

A “bounce” message is a new message that is sent by a receiving MTA, using the Envelope Sender of 
the original email as the new Envelope Recipient. This bounce is sent back to the Envelope Recipient 
(usually) with a blank Envelope Sender (MAIL FROM: < >) when the original message is undeliverable 
(typically due to a non-existent recipient address).

Increasingly, spammers are attacking email infrastructure via misdirected bounce attacks. These attacks 
consist of a flood of bounce messages, sent by unknowing, legitimate mail servers. Basically, the process 
spammers use is to send email via open relays and “zombie” networks to multiple, potentially invalid 
addresses (Envelope Recipients) at various domains. In these messages, the Envelope Sender is forged 
so that the spam appears to be coming from a legitimate domain (this is known as a “Joe job”). 

In turn, for each incoming email with an invalid Envelope Recipient, the receiving mail servers generate 
a new email — a bounce message — and send it along to the Envelope Sender at the innocent domain 
(the one whose Envelope Sender address was forged). As a result, this target domain receives a flood of 
“misdirected” bounces — potentially millions of messages. This type of distributed denial of service 
attack can bring down email infrastructure and render it impossible for the target to send or receive 
legitimate email.

To combat these misdirected bounce attacks, AsyncOS includes Bounce Verification. When enabled, 
Bounce Verification tags the Envelope Sender address for messages sent via your appliance. The 
Envelope Recipient for any bounce message received by the appliance is then checked for the presence 
of this tag. Legitimate bounces (which should contain this tag) are untagged and delivered. Bounce 
messages that do not contain the tag can be handled separately.

    TLS: Required (Verify)

    Bounce Profile: tls_failed

example2.com

    IP Address Preference: IPv6 Preferred

    Maximum messages per connection: Default

    Rate Limiting: Default

    TLS: Preferred

    Bounce Profile: tls_failed