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Greylisting is used to prevent spam from reaching mailboxes.


If you did not select this module to be included during the installation process, you must first install the module.

You can find this feature in the menu system at the following location:

Server|Mail Scanning|Greylisting


Greylisting can dramatically reduce the amount of spam reaching your mailboxes. When the service is enabled, a mail message that is not recognized will be gently rejected. If the mail message is legitimate, the sending mail server will re-attempt subsequent deliveries and the ClearOS server will then accept it. For the most part, spammers do not bother with the second delivery attempt and this results in less spam. The parameters that you can use to fine tune the greylisting engine are described below.


State of the greylisting engine.


The amount of time that must pass before a subsequent delivery attempt is allowed.

Data Retention Time

The greylisting engine keeps track of both mail servers and sender e-mail addresses for a specified amount of time (default is 35 days). If messages from validated sender or server arrives, the greylisting engine will accept delivery on the first attempt. For example, if sends an e-mail to one of your users on a weekly basis, only the very first mail message is delayed. All subsequent messages are delivered automatically since has been validated.

content/en_us/5_greylisting.txt · Last modified: 2015/03/02 09:10 (external edit)