Metrics for Bayesian analysis:
Prob(spam|words)=( Prob(words|spam) X Prob(spam) ) | prob(words)
Exchange server tops the chart in the email server solution among the different technology like Lotus Notes,send mail,Q mail,post fix and many others. I am going to discuss about the spam solution in terms of the exchange server alone. Exchange server product come along with the anti spam solution called IMF(Intelligent message filter). But the solution is 50 out of 100 hence forth we should relay on some anti spam solution product until Microsoft produce some effective add-on solution with the exchange server product itself.
It is better to have anti spam application rather than the appliances.Due to the scalability and manageability reason,server side spam control is obvious.With the multitude of antispam solution for exchange,choosing the right product is not a simple task.Factors to be reviewed while selecting the antispam product to your network is important. Features like Bayesian analysis support, new spam signatures,keyword checking,header checking,SPF(Sender Policy Framework) support,DHA(Directory harvest attack),CCS(Central Checksum Service) bulk email detection,automated whitelist,blacklist,customizable policy for individuals/groups,foreign language spam,Anti-phishing,remote management,email alerts,character set blocking,image spam filter,Log reporting ,disclaimers and signatures.
List of antispam solution:
GFiMailEssentails for Exchange/SMTP
Exclaimer mail utility for exchange server
Surf Control for exchange server
XWall for exchange server
Symantec Mail Security for Exchange
Sybari Advanced Spam Manager
MIMEsweeper Spamlogic anti-spam appliance
Above listed antispam solution will do address your spam issue.
Please do post, if you have any queries.