What Is Greylisting And Why It Should Be Enabled?


Greylisting is an email filtering technique that explicitly targets potential spam emails during delivery. It operates as follows: Emails are sent from a sender to a receiver using the Simple Mail Transfer Protocol (SMTP), the standard email communication method.

Greylisting defends email users against spam. When you enable Greylisting, the mail server will temporarily reject any email from a sender that the server does not recognize. However, if the email is legitimate, the server that sent it will try to send the email again after a delay.


-Effective Spam Reduction: Greylisting is highly effective in reducing spam emails, as it filters out a significant portion of spam by targeting senders who do not retry delivery.

-Resource Efficiency: By temporarily rejecting emails, greylisting helps distribute the load on email servers, improving performance and reducing resource usage.

-Enhanced Email Security: Greylisting adds an extra layer of protection by filtering out suspicious or illegitimate email sources, improving overall email security.

-Adaptive Defense: Greylisting can adapt to new spamming techniques and patterns, making it effective against evolving spamming tactics over time.

-Compatibility with Other Filters: Greylisting can complement other spam filtering techniques, such as content filtering and blacklisting, further enhancing email security.


-Delayed Email Delivery: Greylisting can introduce a delay in email delivery, as legitimate senders must retry their emails after the initial rejection. This delay can sometimes be noticeable and may inconvenience time-sensitive communications.

-Initial False Positives: Greylisting may initially reject legitimate emails from unknown senders, resulting in false positives. However, legitimate senders are expected to retry and deliver the email in subsequent attempts.

-Administration and Management: Configuring and managing greylisting settings may require technical knowledge or administrative effort, especially when fine-tuning parameters such as the greylisting delay period or allowlisting rules.

-Incompatible with Real-Time Communication: Greylisting may not be suitable for real-time communication scenarios where instant email delivery is critical, as it can introduce delays that impact real-time conversations or notifications.

-Greylisting has a couple of associated problems: For greylisting to work effectively, it is crucial that the IP address of the sending SMTP server remains unchanged throughout the email delivery process.

When the sender's IP address SMTP server changes, the recipient's SMTP server will consider the incoming email as unknown, resulting in the email being added to a greylist.

In certain cases, the delivery of emails can fail due to incorrect implementation or configuration of the sending mail server. The email will not be delivered if the request to resend it is not complied with by the sender's mail transfer agent.

Please refer to the following steps to enable/disable Greylisting in WHM.

  1. Log in to the WHM Panel.

  2. Go to the email section and click on the greylisting.

  1. By default, greylisting will be disabled.

  1. You can click the ON button to enable the greylisting.  

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