Cisco Cisco Email Security Appliance C170 Guia Do Utilizador

These features are mutually exclusive.

You can specify the SMTP code and response message for messages with malformed envelope senders, 
for envelope senders which do not exist in DNS, and for envelope senders which do not resolve via DNS 
queries (DNS server might be down, etc.). 

In the SMTP response, you can include a variable, 

$EnvelopeSender

, which is expanded to the value of 

the envelope sender when the custom response is sent.

While typically a “Domain does not exist” result is permanent, it is possible for this to be a transient 
condition. To handle such cases, “conservative” users may wish to change the error code from the default 
5XX to a 4XX code.

The sender verification exception table is a list of domains or email addresses that will either be 
automatically allowed or rejected during the SMTP conversation. You can also specify an optional 
SMTP code and reject response for rejected domains. There is only one sender verification exception 
table per appliance and it is enabled per mail flow policy.

The sender verification exception table can be used to list obviously fake but correctly formatted 
domains or email addresses from which you want to reject mail. For example, the correctly formatted 
MAIL FROM: 

pres@whitehouse.gov

 could be listed in the sender verification exception table and set 

to be automatically rejected. You can also list domains that you want to automatically allow, such as 
internal or test domains. This is similar to envelope recipient (SMTP RCPT TO command) processing 
which occurs in the Recipient Access Table (RAT).

The sender verification exception table is defined in the GUI via the Mail Policies > Exception Table 
page (or the CLI, via the 

exceptionconfig

 command) and then is enabled on a per-policy basis via the 

GUI (see 

) or the CLI (see the CLI Reference Guide for AsyncOS for Cisco Email Security Appliances.

Entries in the sender verification exception table have the following syntax:

See 

 for more information about modifying the exception table.

This section provides an example of a typical conservative implementation of host and envelope sender 
verification.