{TemplateInclude "Default" "HelpNav"}

SMTP Agent - UBE Blocking

This page provides options that block incoming messages from specified sites. These options are designed to protect your messaging system from unsolicited bulk e-mail (UBE) or SPAM.

IMPORTANT: You do not need to restart the smtpd executable to effect changes to these properties. Instead, changes are implemented within 5 minutes.

 

Flags

Block Hosts in Blocked List

Restricts access to your messaging system. If selected, the SMTP Agent refuses connections from any mail host with an IP address designated in the Blocked Hosts list.

 

Deny Hosts Not in DNS

Provides reverse DNS lookups. When receiving messages from external systems, the SMTP Agent verifies that the host’s IP address and domain correspond to its DNS record. If they don’t match, the SMTP Agent drops the connection.

NOTE: You must configure your DNS server to support reverse DNS lookups for this option to function.

 

Override with Authentication

This option provides an exception to the Deny Hosts Not in DNS option. If enabled, hosts that are not listed in DNS are given the opportunity to authenticate with the SMTP Agent before their connection is dropped.

 

RBL Check

Enables the SMTP Agent to do lookups on the Realtime Blackhole List (RBL*). RBL maintains a list of confirmed spammers and open relays. If the mail host matches an entry on the RBL, the connection is refused.

 

RBL Servers

To add an RBL site, type the IP address or host name of the RBL list server in the RBL Servers box and click Save. Enter one RBL server per line.

The RBL entry can include a trailing semi-colon ( ; ) and subsequent text. The text following the semi-colon is displayed as part of the protocol reply informing the sender he is blocked.

The following configuration entry references bl.spamcop.net as the RBL Host and then adds a message directing the sender to the SpamCop web site:

bl.spamcop.net;You have been blackholed by spamcop.net. Please see http://spamcop.net to get removed

If the character sequence %d.%d.%d.%d is provided as part of the text, it is replaced by the IP address of the blocked system. Use this feature to generate responses containing URLs that point directly to the RBL system’s look-up page.

For example, in this configuration entry,

bl.spamcop.net;Please see http://spamcop.net/w3m?action=checkblock&ip=%d.%d.%d.%d

http://spamcop.net/w3m?action=checkblock&ip is the URL format for SpamCop’s lookup page and %d.%d.%d.%d generates the IP address of the blocked host. The resulting protocol reply includes a URL that takes the blocked sender directly to SpamCop’s lookup page and tests his or her IP address.

IMPORTANT: If a percent sign ( % ) is provided as part of the SMTP message text, type it as %%. Using a single percent sign without the letter “d” might crash the SMTP Agent.

 

Blocked Hosts

A list of blocked IP address ranges. If Block Hosts in Blocked List is selected, the SMTP Agent refuses connections from any host within the designated IP address range.

Listing ranges of registered IP addresses blocks specific external hosts from sending mail to or relaying mail through your messaging system. For example, you can choose to list the IP addresses registered to public mail systems (such as Hotmail,* Yahoo,* and Juno*) because spammers frequently use these systems to relay UBE.

Use this option to block internal hosts. By listing ranges of internal IP addresses, you can block specific workstations from sending any messages over the Internet.

To add a blocked host, type a range of disallowed IP addresses in the Blocked Hosts box and click Save. Enter one blocked host per line.

For example:

251.70.2.53-251.70.2.60

 

A trademark symbol (®, TM, etc.) denotes a Novell trademark. An asterisk (*) denotes a third-party trademark. For more information, see Legal Notices.