Руководство Пользователя для Cisco Cisco Email Security Appliance C170

If you want to filter messages based on these headers, you must send the Outbreak Filter processed 
messages back to an Email Security Appliance (by configuring an alternate destination mail host), and 
scan them using a content filter that matches these headers.

If you want to perform a content filter-based scan on the Outbreak Filter processed messages, you must 
configure the Outbreak Filter to send the processed messages back to an Email Security Appliance. This 
is because, in the processing pipeline, the Outbreak Filter scan is performed after the content filter scan.

In the Alternate Destination Mail Host field, enter the IP address (IPv4 or IPv6) or the FQDN of the 
appliance where you want to send the processed messages for further scans.

If the message’s threat level exceeds the message modification threshold, the Outbreak Filters feature 
rewrites all URLs in the message to redirect the user to the Cisco web security proxy’s splash page if 
they click on any of them. (See 

 for more information.) If the message’s 

threat level exceeds the quarantine threshold, the appliance also quarantines the message. If a small 
scale, non-viral outbreak is in progress, quarantining the message gives TOC time to analyze any suspect 
websites linked from possible outbreak messages and determine whether the websites are malicious. 
CASE uses updated Outbreak Rules from SIO to rescan the message to determine if it is part of the 
outbreak. After the retention period expires, the appliance releases the message from the quarantine.

AsyncOS rewrites all of the URLs inside a message except for the ones pointing to bypassed domains.

The following options are available for URL rewriting:

Enable only for unsigned messages. This option allows AsyncOS to rewrite URLs in unsigned 
messages that meet or exceed the message modification threshold, but not signed messages. Cisco 
recommends using this setting for URL rewriting.

The Email Security appliance may rewrite URLs in a DomainKeys/DKIM-signed message and 
invalidate the message’s signature if a server or appliance on your network other than the Email 
Security appliance is responsible for verifying the DomainKeys/DKIM signature.

Enable for all messages. This option allows AsyncOS to rewrite URLs in all messages that meet or 
exceed the message modification threshold, including signed ones. If AsyncOS modifies a signed 
message, the signature becomes invalid.

Disable. This option disables URL rewriting for Outbreak Filters.

You can modify a policy to exclude URLs to certain domains from modification. To bypass domains, 
enter the IPv4 address, IPv6 address, CIDR range, hostname, partial hostname or domain in the Bypass 
Domain Scanning field. Separate multiple entries using commas.

The Bypass Domain Scanning feature is similar to, but independent of, the global whitelist used by URL 
filtering. For more information about that whitelist, see 

.