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What is GreyListing?

Posted by Allura on 18 05 2018.

A Brief Overview

This helps you configure GreyListing to protect the server against any unwanted emails as well as spam. While enabled, the server temporarily rejects any email from sender unrecognized by the server. For legitimate emails, originating server might send it again after a short delay. After a sufficient span of time, the server then accepts the mail.

GreyListing can identify any incoming email by triplet which is a collection of 3 pieces of information – the IP address, address of the sender and address of the recipient. By deferring any unknown triplet, it filters spam while allowing legitimate emails another chance to get passed through.

Before you can have access to Greylisting Configuration Settings as well as Trusted Hosts, and Reports sections of interface, you need to click on/off in order to enable the feature namely Greylisting.

Key Configuration Settings

This tab helps to denote parameters of Greylisting.

You need to execute following steps to use Greylisting.

  • Configuration Settingstab needs to be clicked.
  • Desired values for every setting must be entered. You can also keep default values.
  • Save

Here is the table containing descriptions and values for Configuration Settings.

  • Initial Deferral Time (in minutes)- default value 10 – maximum value 240 ( 4 hours) – This describes total number of minutes during which the feature defers emails from unknown triplet. The time starts as the server receives the initial mail from any unrecognized IP address.
  • Resend Acceptance Period (in minutes) – default value 240 – maximum value 1440 (per day) – This describes the amount of minutes during which the feature accepts any resent email from any unrecognized triplet. The time starts as the server receives the initial mail from any unrecognized IP address.
  • Record Expiration Time (in minutes) – default value 4320 – maximum value 43200 – This describes the amount of minutes the feature removes triplet record while treating any resent email as if it is coming from an unknown triplet. The time starts as the server receives the initial mail from any unrecognized IP address.
  • Bypass Greylisting for Hosts with Valid SPF Records – default value: YES – maximum value: N/A – This describes if the system can accept emails from hosts with valid SPF email validation system. It enables mail exchanges to confirm if a received mail has come from a host authenticated by the administrators of the said domain.

Here is the table to illustrate timeline of incoming email as well as the response of Greylisting with default settings.

One –

  1. First resend attempt – N/A
  2. Response – Defer emails back to the sender

Add triplets to the database of Greylisting

Multiple –

  1. First resend attempt – within first 10 mins of initial emails
  2. Response – Continue deferring emails back to the sender until expiry of

 

Initial Deferral Time

Multiple – 1. First resend attempt – 10+ mins after the first email

  1. Response – Deliver emails to the respective recipients

Continue delivering emails from the triplet until expiry of

 

Record Expiration Time –

Multiple– 1. First resend attempt – 240+ mins after the first email

  1. Response – Treat emails as if it has been sent by an unknown triplet