Add the line 1.2.3.4:deny,RBLSMTPD=" - Connections refused" to your tcp.smtp file. The RBLSMTPD message is optional.
Not optional, useless. When you deny the connection you can't send back a message. I believe what you want is either:
1.2.3.4:deny
or
1.2.3.4::allow,RBLSMTPD="-Connections refused"
-- Lou Hevly Manresa, Catalonia http://visca.com
