Руководство Пользователя для Cisco Cisco Email Security Appliance C170
Chapter 6 Using Message Filters to Enforce Email Policies
6-140
Cisco IronPort AsyncOS 7.5 for Email Advanced Configuration Guide
OL-25137-01
Message Filter Examples
This section contains some real world examples of filters with a brief discussion
of each.
of each.
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
IronPort 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
often used to exploit traditional Sendmail/Qmail systems. As many of these
symbols (for example
%
) can be part of a perfectly legal email address, IronPort
appliances will accept these as valid addresses, verify them against the configured
recipient lists, and pass them on to the next internal server. IronPort appliances do
not relay these messages to the world.
recipient lists, and pass them on to the next internal server. IronPort 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.
that are misconfigured 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.
sourceRouted:
if (rcpt-to == "(%|@|!)(.*)@") {
bounce();
}