What is greylisting?
You are probably familiar with blacklisting, where certain entities are denied access to a service, and with whitelisting, where specific entities are granted exclusive access by lifting normal security measures. But what does greylisting mean?
What does greylisting involve in general?
Broadly speaking, greylisting refers to a procedure used to protect email against unwanted messages.
How can you identify spammers?
Spammers often send messages to generic email addresses without having a specific user database. They ‘shoot in the dark’ by targeting common names and prefixes, such as Anna@… or mail@…, which are often used with popular domain names. Many of these recipients do not even exist. As a result, spammers receive lots of bounced, undelivered messages, but they rarely try to resend them because they do not perform any error checking.
What is the difference from normal outgoing mail servers?
The difference between a spamming server and a regular outgoing mail server lies in how it responds. While a regular server actively tries to resend undelivered messages (without always notifying the user), a spamming server usually ignores undelivered messages.
The greylisting technique
Greylisting recognises this difference in behaviour between outgoing mail servers and adjusts the behaviour of the incoming mail server accordingly. When a message is received for the first time, it is automatically rejected and the greylisting server waits for a new attempt. On a second attempt to send the same message, the server accepts it because it does not appear to come from a spam source. In addition, the server places the sender on a temporary whitelist. The more messages are successfully received from the same sender, the more the server trusts that sender.
Does kyzoe.be support greylisting?
Greylisting is an effective spam-filtering technique and is implemented at infrastructure level, so it cannot be enabled or disabled for individual accounts. Almost all hosting providers, including Kyzoe.be, use greylisting nowadays.
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