Cisco Cisco Email Security Appliance C160 Mode D'Emploi
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User Guide for AsyncOS 10.0 for Cisco Email Security Appliances
Chapter 9 Using Message Filters to Enforce Email Policies
Message Filter Examples
Message Filter Examples
This section contains some real world examples of filters with a brief discussion of each.
Related Topics
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Open-Relay Prevention Filter
This filter bounces messages with addresses using
%
, extra
@
, and
!
characters in email addresses:
•
user%otherdomain@validdomain
•
user@otherdomain@validdomain:
•
domain!user@validdomain
Cisco appliances are not susceptible to these third party relay hacks that are often used to exploit
traditional Sendmail/Qmail systems. As many of these symbols (for example
traditional Sendmail/Qmail systems. As many of these symbols (for example
%
) can be part of a perfectly
legal email address, Cisco appliances will accept these as valid addresses, verify them against the
configured recipient lists, and pass them on to the next internal server. Cisco appliances do not relay
these messages to the world.
configured recipient lists, and pass them on to the next internal server. Cisco appliances do not relay
these messages to the world.
These filters are put in place to protect users who may have open-source MTAs that are misconfigured
to allow relay of these types of messages.
to allow relay of these types of messages.
Note
You can also configure a listener to handle these types of addresses. See
for more information.
Policy Enforcement Filters
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sourceRouted:
if (rcpt-to == "(%|@|!)(.*)@") {
bounce();
}