This article is related to the Anti-Spam Filtering Tool add-on for cPanel accounts.
The Anti-Spam filter uses a variety of filtering methods that involved checking the sender's IP address against public and private blacklists. This determines if the IP reputation of the sender is positive. The spam filter also verifies the sending e-mail server following RFC standards via the use of "greylisting." Messages are also filtered for phishing attempts, viruses, and general "spam-like" characteristics.
If a message is sent and does not arrive in your inbox, please note that it may have been caught in the "greylist." If so, the sending server (if properly configured) should attempt to re-deliver the message automatically over a period of time.
If the message needs to be re-delivered sooner, have the user manually retry after 10 minutes. Note that you may receive both copies after their server automatically retries the first.
If messages are not delivered after a period of hours, log into your spam filtering dashboard and check for that message in the spam quarantine.
Any message that is blacklisted or permanently deferred should appear in the spam quarantine. Messages containing potential viruses will not appear in the quarantine.
Messages CAN be released from the quarantine for successful delivery to your inbox. The filter will adjust according to what you release through the quarantine over time.
Further information on the Anti-Spam Filtering Tools can be found here.