FreeBSD VPS v2/v3: Sendmail RBL
 NOTE: Any spam-filtering technique may also block legitimate email messages. We strongly recommend the spam blocking technique described here because it is very effective. However, it is not guaranteed to block all spam. Some spam may pass through filters, and some legitimate email may be blocked.
The Sendmail RBL is one of the most powerful tools you can use to stop unsolicited commercial email (UCE, or spam). Spam and viruses represent a large problem for email users and administrators. Several methods attempt to filter spam and viruses at both the server and email client level. Using Sendmail RBL along with spam filters such as SpamAssassin and virus filters such as ClamAV comprises a comprehensive solution to filter unwanted emails. Effective spam and virus filters eliminate the problem as early in the email delivery process as possible. Sendmail RBL eliminates spam from known spammers at the earliest point possible in email delivery: upon the initial SMTP connection. Because Sendmail RBL filters spam upon the initial connection, enabling this configuration will improve the overall performance of your server.
Sendmail RBL configures your email server to check the IP address of incoming email connections against lists of known spammers' IP addresses. The email server then immediately rejects offending connections before harmful email is accepted or delivered. The Sendmail RBL vinstall offers the ability to easily configure your server's Sendmail email server to subscribe to several of these lists, called RBL's (or real-time blackhole lists). When you enable this feature, remote email servers listed on one of these RBL's which attempt to connect to your email server will have their connection rejected immediately with the following error message:
553 5.3.0 Rejected - see http://domain.com
where domain.com indicates a Web site with more information about the RBL and why the IP address is being blocked.
The Sendmail RBL vinstall helps you easily configure Sendmail for both subscription to and/or unsubscription from one or more lists. The available RBL's include:
- sbl-xbl.spamhaus.org » Spamhaus block list. SBL and XBL (Recommended)
- sbl.spamhaus.org » Spamhaus block list (SBL)
- xbl.spamhaus.org » Spamhaus block list (XBL)
- list.dsbl.org » Distributed Server Boycott List (DSBL)
- multihop.dsbl.org » Distributed Server Boycott List (DSBL)
- dnsbl.ahbl.org » List against abusers and spammers (AHBL)
- dnsbl.njabl.org » Not Just Another Bogus List (NJABL)
- unconfirmed.dsbl.org » Distributed Server Boycott List (DSBL)
- whois.rfc-ignorant.org » RFC Ignorant (Whois)
- dnsbl.sorbs.net » Spam and Open Relay Blocking System (SORBS)
The Spamhaus SBL-XBL Block List RBL is the default and recommended list. You can subscribe to as many lists as you wish, however, each list has strengths and weaknesses. Also, subscribing to multiple RBL lists will have a cumulative effect and filter email more aggressively with each list added. Many RBL lists were developed for a specific purpose or to address a specific spam problem. Research each list you consider before subscribing to it. Links to more information are available at the end of this page.
Installation and Usage
To use the Sendmail RBL vinstall to manage your Sendmail subscriptions to real-time blackhole lists, use the following steps:
- Connect to your server through SSH,
su to root, and execute the following command from the prompt:
# vinstall sendmail-rbls
The screen lists the available RBL lists and whether or not Sendmail is currently subscribed to any list.
- The vinstall utilizes a toggle-style interaction. Type the number of the list you wish to subscribe to or unsubscribe
from and press Enter. You can only select one list at a time.
- The vinstall makes backup copies of the existing
/etc/mail/your.hostname.mc and
/etc/mail/your.hostname.cf files, named /etc/mail/your.hostname.mc.bak and
/etc/mail/your.hostname.cf.bak, respectively (where your.hostname is the hostname of your
account). It then recompiles the Sendmail configuration file to configure subscription to the RBL lists selected and
restarts Sendmail.
- Select another list if desired and press Enter.
- Press q to exit the vinstall.
More Information
For more information about RBL's and other spam-fighting techniques, visit the following pages:
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