How do I get SpamAssassin to stop using a blacklist to block or reject email?

SpamAssassin is rarely set up to actually reject email, so people asking this question usually have a problem with their mail server configuration, not SpamAssassin. Remove the option to reject email with a blacklist from your server configuration.

An example rejection message from postfix looks like this, in /var/log/mail.log:

Feb 2 10:44:44 panic postfix/smtpd[17332]: NOQUEUE: reject: RCPT from lab75-4-82-245-152-54.fbx.proxad.net[82.245.152.54]: 554 5.7.1 Service unavailable; Client host [82.245.152.54] blocked using zen.spamhaus.org; http://www.spamhaus.org/query/bl?ip=82.245.152.54; from=<ciohev7300@proxad.net> to=<si_oz@chaosreigns.com> proto=ESMTP helo=<proxad.net>

That is caused by the following line in /etc/postfix/main.cf:

reject_rbl_client zen.spamhaus.org

There is nothing wrong with rejecting email in this manner, but it is something that people do often ask how to do.