Spam Guard In Postfix

The most effective approach to spam prevention is to keep off of lists where spammers might find your e-mail address.
A Directory Harvest Attack (DHA) is when a spammer bombards a domain with thousands of generated email addresses in an attempt to collect valid email addresses from an organisation.
Spam recipients who use Exchange-based mail services are at a relative disadvantage in tracing spam messages, since Exchange clients often make it difficult to see SMTP headers.
It may have some of the same capabilities as a mail transfer agent, but is mainly used for pop3 or imap mail pickup, and may add special capabilities such as spam filtering.
A spam filter is a process that examines a stream of incoming mail messages and sorts them into those that may be spam and those that probably aren't.
ROKSO (Registry of Known Spam Operations) is an extensive database of spam perpetrators and support operations, maintained by The Spamhaus Project.
If you use outlook it is suggested you get a spam blocker.
Spam has come to mean unsolicited commercial email (uce) which is also known as bulk email.

spam guard in postfix