Using an MTA (Message Transfer Agent) in combination with SpamAssassin gives you a powerful spam detection solution capable of identifying unwanted emails in advance and rejecting them before needing to deal with them manually.

SpamAssassin can be utilized by other apps/services for evaluating emails to determine the probability of whether it is unwanted or not. SpamAssassin requires an additional mail-routing program capable of interpreting the results from SpamAssassin.

SpamAssassin includes the following components as executable Windows applications (exe.)

spamassassin.exe: Mail filter
spamd.exe: SpamAssassin as a server process (Daemon)
spamc.exe: Client for server process
sa-update.exe: A program to update filter-rule-settings
sa-learn.exe: Trains the Bayes-Filter in regards to spam-/ham-mails