Greylisting

This action is valid for the following senders: External.

Greylisting is a precautionary measure against "suspicious" emails. If emails remain just below the spam threshold you defined, without greylisting these emails would be rated as sufficiently safe.

The greylisting action does not let this email pass immediately, but temporarily rejects it. The sending email server receives an error message instructing it to resend the email after a certain amount of time. The email will then be delivered again. You can set the time at which the submitting server may perform a second attempt.

Greylisting is based on the following principle: A spammer usually saves himself the effort of sending a second email. A regular sender, on the other hand, will try to have the email delivered again after some time. On the second attempt this connection is now considered to be of higher value, resulting in the email being allowed to pass. You can individually set the threshold for the number of penalty points that determines when emails that pass are still classified as suspicious.

  1. Open a rule for inbound emails.
  2. Switch to the Actions tab.
  3. Click Add and select the Greylisting action.
  4. Click Select and close.
    The configuration dialog opens.
    Configuring the greylisting options
  5. Specify,
    • the threshold value for activating greylisting and
    • the period of time after which emails are unblocked again.
  6. Optional Check the box if you want to block untrusted emails with attachments regardless of the spam confidence level.

NOTE: The greylisting threshold must be lower than the spam threshold, otherwise greylisting will not work.