How does the SpamAssassin for Exchange Server stops spam emails?
SpamAssassin is an anti-spam software. It sorts out unwanted emails automatically. The Exchange Server Toolbox comes with a preconfigured SpamAssassin - no additional preparations necessary. The spam security is increased if you train SpamAssassin regularly (mark any spam email that slipped through your defenses as spam and "good" emails as ham).
The SpamAssassin modules rate emails according to various criteria. The results are added and result in an internal value, the SpamScore. A high SpamScore means a high probability that an email is, indeed, spam.
1. Static analysis
Regular expressions are used to rate the content and attachments of an email. This way, suspicious words are detected even if the spelling was changed to mask them. SpamAssassin will mark variants, even if they differ from the norm:
2. Network analysis
SpamAssassin creates a checksum of the email content and compares it to the Razor2 network. Sender addresses are checked via DNS RBL (real time blacklist server) and DNS whitelists, links within the emails are compared to URL RBL (website real time blacklist server).
3. Learning Bayes filter
In a statistical analysis words and word constellations are evaluated mathematically and rated according to the probability that they are spam. Using the train function of the Exchange Server Toolbox Outlook Add-In the Bayes filter can be improved continuously.
How was SpamAssassin integrated into the Exchange Server Toolbox?
SpamAssassin works as a condition in the rule system. The system works just like the rule system in Outlook: if certain conditions are met, the program triggers a predefined action.
In the Exchange Server Toolbox the SpamScore of each email is compared to predefined values. Depending on which thresholds are crossed the email will be marked as possible spam and delivered or refused entirely (Exchange Server 2007 and higher). Of course you can tailor the rules defining how spam will be treated to your needs.
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