Setting Up Spam Protection
To protect your users from spam, you can use the following tools with your control panel:
- SpamAssassin spam filter. It is a powerful spam filter that uses a wide variety of local and network tests to identify spam signatures.
You can configure the spam filter so as to either delete suspicious messages when they come to your mail server, or change the subject line and add "X-Spam-Flag: YES" and "X-Spam-Status: Yes" headers to the messages. The latter can be useful for users who prefer to filter mail with mail filtering programs installed on their own computers.
To learn more about SpamAssassin, visit http://spamassassin.apache.org.
To configure and switch on the SpamAssassin filter, proceed to the Setting Up SpamAssassin Spam Filter section.
- DomainKeys. DomainKeys is a spam protection system based on sender authentication. When an e-mail claims to originate from a certain domain, DomainKeys provides a mechanism by which the recipient system can credibly determine that the e-mail did in fact originate from a person or system authorized to send e-mail for that domain. If the sender verification fails, the recipient system discards such e-mail messages. To configure the DomainKeys system on your server, refer to the section Switching on Spam Protection Based on DomainKeys.
- DNS blackhole lists. This spam prevention system is based on DNS queries made by your mail server to a database, which contains known and documented sources of spam, as well as an extensive listing of dynamic IP addresses. Any positive response from this database should result in your mail server returning a '550' error, or rejection of the requested connection.
To configure your mail server for working with DNSBL databases, proceed to the Switching On Spam Protection Based on DNS Blackhole Lists section.
- Sender Policy Framework (SPF). This spam prevention system is also DNS query-based. It is designed to reduce the amount of spam sent from forged e-mail addresses. With SPF, an Internet domain owner can specify the addresses of machines that are authorized to send e-mail for users of his or her domain. Receivers that implement SPF then treat as suspect any e-mail that claims to come from that domain but fails to come from locations that domain authorizes.
To learn more about SPF, visit http://www.openspf.org/howworks.html.
To enable filtering based on SPF, proceed to the Setting Up Support for Sender Policy Framework System section.
- Server-wide black and white lists. Black and white lists are standard mail server facilities. You can use the black list to specify the domains from which mail must not be accepted, and white list to specify the IP addresses of machines or networks from which mail must always be accepted.
To set up server-wide black and white lists, proceed to the Setting Up Server-wide Black and White Lists section.