Preventing Spam Mail

  

Figure 4.21: The Spam Mail Filtering Setup Screen

Apart from the `Reject Invalid Senders' option in the Mail Setup screen, the firewall offers additional measures that can be used to block unsolicited junk e-mail (spam mail). You can use the MAPS RBL (Mail Abuse Prevention System Realtime Blackhole List; see www.mail-abuse.com for details) or other RBLs, as well as create your own blacklist. You can also set up exceptions to the blacklist rules.

The fields in the Spam Mail Filtering Setup Screen (Figure 4.21) are:

Use RBL

The firewall can refuse mail from hosts that are listed in a Realtime Blackhole List (RBL), such as the MAPS (Mail Abuse Prevention System) RBL. This toggle enables or disables this feature.

RBL Domain Name

This field lets you specify the domain name associated with the RBL that you want to use. For the MAPS RBL, use `blackholes.mail-abuse.org'.

The available keys are:

F1

Cancel changes and return to the Mail Setup Screen

F2

View or edit the list of spamming hosts/domains

F3

View or edit the list of addresses excluded from spam filtering

F7

View help

F8

Save changes and return to the Mail Setup Screen

  

Figure 4.22: The Reject Spamming Mail Hosts Setup Screen

The Reject Spamming Mail Hosts Setup Screen (Figure 4.22) lets you specify a set of host or domain names. When mail arrives from a sender whose address is in a domain in the list, or whose name server is in a domain in the list, the mail will be rejected. Similarly, the `Received:' headers are checked to see if the mail was relayed through such an offending host.

  

Figure 4.23: The Spam Domain Exempt Sender Setup Screen

The Spam Domain Exempt Senders Setup Screen (Figure 4.23) lets you specify a set of e-mail addresses that will be accepted as mail senders even if the domain is a spamming domain. This can allow you to block domains but allow a few legitimate users through. This is particularly useful for selectively blocking free e-mail services, such as HotMail, which are frequently abused by mail spammers.