What is Greylisting? How does it work?


What is Greylisting?

Greylisting is an anti-spam technology practiced by mail servers to prevent spam. The receiving mail server determines the sender, to please retry to send the email again in X minutes.

How does Greylisting work?

A well-configured mail server will attempt to resend an email at different intervals until it’s accepted or denied by the receiving mail server.

There are many types of greylisting, but the most popular is time-based greylisting as mentioned above. Each mail server has a different time they greylist the sender for, per email, usually between 1 and 15 minutes.

Greylisting Technology

Clearalist deploys break-through anti-grey-listing technology. When we encounter any greylisting we will wait a few minutes and retry to validate those specific emails. This decreases the amount of “Unknowns or Mailbox” you will receive back from us. So you wait a little longer for your results, but your results will be a lot better.

It doesn’t matter how many greylisted email addresses you upload to be validated, whether it’s 1000 or 100,000. The processing is only delayed by just a few minutes.


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