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ISMail EP eliminates spam with up to 7 levels of almost fully-automated defenses.
Because no single method is effective at removing all spam, ISMail EP integrates a combination of internal, external, and configuration-related techniques to provide nearly spam-free mailboxes without the manual user 'training' required by many spam blockers.
The anti-spam system is equally effective for local mail domains, and for remote domains when ISMail serves as a backup or relay.
Level 1: Network connections are refused from all 'Blocked IPs'. If an IP is blocked, the sender can not even establish a network link to ISMail.
Level 2: Blacklists are scanned to determine if the sender IP, domain name, or account name are banned. If so, ISMail returns an error to the sender before any mail is transferred. (Whitelists are also consulted to determine if the sender is known-good, in which case mail can immediately be transferred).
Level 3: Reverse DNS checking is performed to determine if the sender is trying to hide its identity. If so, ISMail returns an error to the sender before any mail is transferred.
Level 4: Real-time blackhole lists (RBLs, CBLs, XBLs, etc.) are consulted to determine if the sender is a known source of spam, viruses, worms, or other malware. Open proxies, hijacked servers, and other non-legitimate mail sources are also checked. If the sender is listed, ISMail refuses to accept any mail.
Level 5. Greylist processing determines whether the sender is 'known' to the receiver. If not, ISMail termporarily refuses to accept mail, indicating that a retry must occur at a later time; this discourages 'hit-and-run' spam attacks from 'bots' and other sources.
Level 6: Content filtering is performed to compare messages with known patterns of spam. If a match occurs, the message is deleted or flagged for further processing by an email client filter.
Level 7: Heuristic filtering with SpamAssassinTM. Includes SURBLs for phishing links and auto-learning for Bayesian probabilistic filtering.