Reject 98% of SPAM with Postfix configuration rules

My spam traffic has decreased to minimum after I've inserted following lines in /etc/postfix/main.cf file (Postfix main configuration file). These settings made my SMTP server to spam resist. This method use DNS queries, what mean very fast UDP communication and use less memory and CPU then any spamfilter. If your hardware is weak or an all-in-one server than use this really fast and effective method.

Before: I received 200-300 spam a day.
Now: I receive only 1-2 unsolicited email a day.

## spam config (requirements: Postfix 2.0 or above) ##
 
#
# reject black listed clients:
# reject_unknown_client value not recommended, because it may causes mail losing.
#
smtpd_client_restrictions = permit_mynetworks, 
reject_rbl_client zen.spamhaus.org,
reject_rbl_client dnsbl.sorbs.net,
reject_rbl_client list.dsbl.org,
reject_rbl_client multihop.dsbl.org
 
 
#
# Requiring this will stop some UCE software. 
# (UCE = Unsolicited Commercial Email = SPAM)
#
smtpd_require_helo=yes
 
#
# Reject the request when the client HELO or EHLO parameter has a bad hostname syntax.
# reject_unknown_hostname value not recommended, because it may causes mail losting.
# (for example: after paypal.com registration you don't receive activation mail! I've tried it.)
#
smtpd_helo_restrictions = permit_mynetworks, reject_invalid_hostname
 
#
# Reject the request when the sender mail address has no DNS A or MX record.
#
smtpd_sender_restrictions = reject_unknown_sender_domain
 
#
# against to open relay:
#
smtpd_recipient_restrictions = permit_mynetworks, reject_unauth_destination
 
## end spam config ##

These easy steps are not require any additional software installation. If you have got Postfix SMTP server, make these changes for decrease your server loading and unnecessary network traffic.

You can find more info about Postfix UCE config rules on Postfix documentation.