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What is Greylisting and how does it work?

What is Greylisting and how does it work?

What is Greylisting?

Greylisting is a powerful Anti-Spam technology that is used to detect if the sending server of a message is RFC compliant. This is done through temporarily blocking unknown senders and caching details of the initial message. Since a majority of SPAM Servers or SPAMBots are not, large volumes of unwanted emails can potentially be filtered during SMTP transmission. Compliant Sending Mailservers, however, will resend the message after a short delay and it will be permitted.

How does Greylisting work?

When a message from an unknown sender arrives, it will be initially blocked by Greylisting and the "Triplet" information cached. This block is in the form of a temporary 451 Error being returned to the Sending Server. This temporary error is considered by this server to be a "Delivery Delayed" notification and will resend the message after a period of time set by Exchange. (Default: 15 Minutes).

When the message is resent, it's "Triplet" is found in the Greylisting Cache and the message is passed to the remaining filters. Items in this cache have a 24 hour lifetime so non-frequent senders may experience the delay more than once.

What is contained in a Greylisting Triplet?
The Greylisting Triplet caches the following information from senders:

  • The Sending Server's IP Address
  • The Message's Envelope Sender
  • The Message's Envelope Recipient

To enable or disable Greylisting on an email address, perform the following steps:

  1. Login to your Jolis Dashboard.
  2. Go to My Email >> Email Accounts
  3. Modify one or more email addresses
  4. Click on/off to enable or disable Greylisting

Note: The Delay before a message is resent is determined by the SENDING server