Greylist

A greylist (also: greylisting) is a method of combating spam in e-mail systems. An email server is temporarily placed on a “gray list” if it attempts to send an email to a recipient with whom it has not yet communicated. In this case, the e-mail is rejected for the time being and the server is informed that it should try again later.

The aim of greylisting is to block unwanted emails from spam bots, which often do not retry delivery, while legitimate email servers do. The grey list allows the recipient server to recognize legitimate email servers and distinguish them from spambots by waiting for legitimate email servers to attempt delivery again.

Greylisting is an effective method of reducing the proportion of spam emails in a system. However, it can also lead to delays in the delivery of legitimate emails, as the sender’s server needs additional time to try to deliver the email again.

It is important to note that greylisting is only one of many spam-fighting methods and that it is not the only solution to spam problems. Other methods such as filtering emails based on content or sender may also be required to create an effective spam management system.