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What Makes Advanced Anti-Spam Software More Effective?

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Advanced anti-spam software contains mechanisms not usually incorporated into standard email filters that are effective at increasing the spam detection rate (often to beyond 99.9%) and mitigating email-borne threats. Typically these mechanisms include Greylisting, SURBL/URIBL filtering and SMTP controls. The function of each is again described below:

Greylisting is a process in which emails are returned to the server from which they were sent with a request for the email to be resent. Spammers´´ servers are often too busy to respond to the requests and the spam email is never returned. This process prevents spam from “not-yet-known” sources being delivered.

SURBL/URIBL Filtering    
SURBL and URIBL filtering provides protection against phishing attacks by rejecting, quarantining or flagging emails that include malicious URLs or links to websites that have been identified as suspicious in previous spam emails. Like RBL lists, these filters are updated frequently by anti-spam software providers.

SMTP Controls    
SMTP controls perform tests to authenticate the sources of emails and their configurations. The controls can be set to reject emails from non-fully qualified domains, from non-fully qualified MAIL FROM commands, and from those with no DNS A or MX record. Exclusions can be created if necessary.

One potential issue with Greylisting is the time it takes for business-critical emails to be returned to spam filter to be processed by the secondary mechanisms of the anti-spam software. Usually the process may delay email delivery by up to a minute but, in extreme cases, it could take as long as twenty minutes for the originating server to respond to the request for the Greylisted email to be resent.

In order to overcome this potential issue, businesses can whitelist email addresses and domain names so emails originating from the whitelisted source bypass the Greylisting process. Excessive use of the whitelisting process should be avoided, as a spammer could take control of a contact´s trusted email account at any time and use the account to send spam emails from a source with a good IP reputation.

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