Once you have the blackist installed, here's how to test whether it's working or not. Start up the "telnet" program (included in Windows and all Unix flavors) with the command:

telnet {your_mail_server} 25

Your mail server will send back a banner something like:

220 mymailserver.com - Welcome to our Sendmail ESMTP

and it will sit waiting for you. Now we'll feed it the first few lines of an SMTP exchange (you type the lines starting with capitals):

MAIL FROM: martha@sendmails.com
250 ok
RCPT TO: {a_valid_email_address@your.domain}
553 sorry, your envelope sender is in my badmailfrom list (#5.7.1)
QUIT
221 mymailserver.com - Goodbye

In this case, we tried to send mail from an account at a known spammer; sendmails.com. We then told the mail server where the mail needs to go. The mail server then told us that it can't accept mail from sendmails.com because we'd correctly installed the qmail block list.

If, however, you have the blacklist installed in your spam filtering program, instead of giving you a 553 error, the mail server will likely allow you to continue feeding in the message with a prompt like:

250 {a_velid_email_address@your.domain}... Recipient ok

DATA
354 Enter mail, end with "." on a line by itself
From: martha@sendmails.com
Subject: Test mail for blacklist

This is a test message
<a href="http://www.sendmails.com">www.sendmails.com</a>
.
250 2.0.0 i3L3v5c23955 Message accepted for delivery
QUIT
221 mymailserver.com closing connection

The mailserver gives the 354, 250, and 221 lines, you type the rest.

Now go back to your mail software and take a look at the spam score assigned by your spam filter. Look at the list of reasons why it's marked as spam; does it mention the sa-blacklist? Does it say the domain was found on the RBL at surbl.org? If so, the spam filter is successfully using the blacklist.