Kerio Server Side Anti-Spam Features
Directory Harvest Attack Protection
Directory Harvest Attacks abuse the design of the SMTP protocol. When one mail server attempts to deliver a message to another mail server, it first inquires whether the recipient address exists on the target mail server. If it exists, the target mail server sends a confirmation; if not, the server responds with negative answer. Spammers take advantage of this communication by submitting multiple requests with different combinations of first and last names. By harvesting valid responses, spammers get very precise list of valid email addresses suitable for future spamming.To fight directory harvest attacks, Kerio MailServer tracks the number of failed recipients during a conversation with the sending mail server. If a predefined threshold is met, the offending mail server will be blocked for a period of one hour.
Spam Repellent
Spam Repellent helps fight off spam zombies and viruses by delaying replies during the SMTP handshake.Since spam mailers and viruses are very impatient when it comes to SMTP communication, they don't wait if the replies from a target mail server are not timely, and simply move on to try another target. By injecting an artificial time delay of a couple of seconds into the SMTP handshake, Kerio MailServer may filter up to 60-70 percent of spam and viruses without ever receiving the messages for analysis.
SpamAssassin
SpamAssassin is a powerful anti-spam engine integrated into Kerio MailServer that identifies junk email. Combining several technologies, SpamAssassin ensures that bulk spam email is properly captured and legitimate email is reliably delivered.Heuristic Engine
Using the heuristic engine in SpamAssassin, each email message is analyzed against multiple anti-spam rules and gives it a numerical rating based on which rules were matched. If the message rating exceeds the spam threshold, the message is marked as spam and then filtered according to the user's wishes.Bayesian Filter
To further increase the success rate and tailor the spam filter to the individual needs of every company, Kerio MailServer allows Outlook and WebMail users to easily train the Bayesian filter in SpamAssassin for every email message that is miscategorized. The Bayesian filter can also be trained by dragging and dropping email in or out of Kerio's Junk E-mail folder in Apple Mail or any other IMAP email client. SpamAssassin then compares incoming messages to spam messages reported by other users, and sees how similar they are to those reported messages.Underlying Technology
SpamAssassin is an anti-spam technology from the open-source Apache SpamAssassin Project.(www.spamassassin.org).
Dual Filtering Policies
Dual filtering policies give administrators the ability to tag messages with low spam score as spam and forward them to user's Junk Email Folders, whereas messages with really high spam score can be automatically discarded without ever reaching user's mailbox. Discarding emails with high spam scoring can help save hard drive space and reduce the amount of emails that endusers need to audit.SURBL Blocking
Similar to RBLs, SURBL (Spam URI Realtime Block Lists) will block messages that contains URIs (usually Web sites) in the message body that links to known spam hosts.Real Time Blacklist Support
Checks sender's IP address for each incoming SMTP connection. If the IP address is in the database of open-relay servers identified as spammers, the incoming email is refused.SPF Verification
Just like Caller ID, SPF (Sender Policy Framework), an emerging standard for domain authentication, helps counter forged "From" addresses in email. Using SPF in Kerio MailServer provides better guarantee that the email came from the domain that it asserts it came from.SPF requires the owner of an Internet domain to modify DNS records and specify which servers are authorized to transmit e-mail for that domain.
Microsoft Caller ID Verification
Using Microsoft Caller ID anti-spam technology, Kerio MailServer checks whether an incoming email is actually being sent by the authorized mail server for that domain (hence the name, Caller ID). Kerio MailServer will decline all email messages with forged "From" addresses.As a side effect, publishing own Caller ID also helps companies protect their reputation by eliminating the possibility of having their domain name hijacked for spam purposes.
To try Caller ID, just visit www.kerio.com/callerid and enter a mail domain in the search field.
