1 Answers
Context filtering is an anti-spam / mail policy method that does not deal with the contents of the mail but rather uses the context of the SMTP connection to decide whether a mail will be accepted or not.
This method usually prevents reception of an e-mail in the first place; thus, common anti-spam features like quarantine, redirect or delete can not be applied. This method also distorts statistics of anti-spam programs because it is usually unknown how many mails would have been received through a certain connection.
Filtering by context includes methods like DNSBL lookups, domain or IP blacklists, etc. This method has an extremely low rate of false positives and false negatives.
On the plus side, this method is usually saving bandwidth and server utilization.