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28 Administrator’s Guide SurfControl RiskFilter - E-mail V5.2.4
S
YSTEM
S
ETTINGS
Receive Settings
2
RBL
Real-Time Blacklist (RBL) checking verifies the validity of message senders. If a sender is listed on an
RBL, they will be prevented from sending messages to your internal MTA.
Reverse DNS enables you to make sure that e-mails sent to your RiskFilter server, are from legitimate
domains. RiskFilter will stop them from sending e-mails to your internal MTA if reverse DNS fails (i.e. the
sender is not from a legitimate domain). The default setting is not to perform a Real-Time blacklist (RBL)
check so this function will need to be enabled if you want to use it
.
RiskFilter will close the connection if reverse DNS lookup fails to validate the host. If you choose to enable
Reverse DNS you must be aware that it may affect the performance of the RiskFilter server, causing
legitimate users to be rejected. To obtain more RBL servers, visit: http://www.declude.com
SMTP Greeting Delay
You can specify that a SMTP greeting message is delayed for a specified time so that if a client tries to
send data ahead of this time, the connection is dropped. This helps to prevent spam, as spam sending
applications send a lot of messages very quickly. The connection is dropped as soon as a message is sent
to the SMTP server before it is ready. This feature is disabled by default.
Allow Access List
Allow Access List enables you to specify an IP address or a group of IP addresses as trusted IP
addresses. This enables them to bypass RBL checks and SMTP greetings.
To create an Access List:
1Select Receive Settings > Connection Control from the System Settings tab.
2 Enter the maximum connections allowed per IP into the’ Simultaneous connections per IP’ field. The
default setting is 100.
3 Enter the maximum number of connections allowed on the RiskFilter server into the Simultaneous
connections on each server field. The default setting is 500.
4 Enter the maximum length of time for timeout in seconds into the Timeout field.
5Select the Perform real-time black list (RBL) check check box. to enable RBL checking, then enter
the network address of the blacklist provider into the Real-Time black list service provider field.
6Select Perform reverse DNS lookup on every incoming connection to enable reverse DNS lookup.
7 Select the Enable SMTP greeting message delay check box.
8 Enter the number of seconds that you want the SMTP server to wait before it displays the SMTP
greeting SMTP greeting, into the Delay the SMTP greeting message to untrusted clients for _
seconds field.
9 Enter the trusted IP address or IP address range into the IP or subnet address field.
10 Click Add to add an IP address or range to the address list on the right. If you want to delete an IP
address or address range in the list, select the IP address or address range then click Remove.
11 Click Submit to put the new settings into effect or Reset if you want to cancel the modifications made
to the current settings.