You can use free and paid subscription blackhole lists with your server.
To switch on spam protection based on DNSBL:
- Go to Tools & Settings > Mail Server Settings (in the
Mail group). - Select the Switch on spam protection based on DNS blackhole lists
checkbox. - In the DNS zones for DNSBL service input box, specify the host
name that your mail server should query, for example:
sbl.spamhaus.org. - Click OK.
Now, email messages from known spammers should be rejected with an error
code 550 (connection refused).
Note: If you use the Qmail mail server and switch on DNSBL, senders with IP
addresses from the blackhole list will not be able to send email even
if they pass SMTP authentication. To avoid this problem, switch on
the message submission as described in the section Configuring
Server-Wide Mail Settings.