What is Greylisting nd how does it reduce Spam?

What is greylisting?

Greylisting is a term used to describe a spam-blocking method. Greylisting blocks spam at the mail server level, and is based on the behaviour of the sending mail server rather than on the content of the message.

How does greylisting work?

Any new email message that is seen by the Expat Email mail server for the first time is temporarily rejected for delivery. Sending mail servers that are properly configured will send the message again, typically within a short time. When the second delivery attempt is made, the Expat Email mail system will accept the message and record in a database that this mail server is legitimate. Any future email messages sent from this particular server will be delivered without delays for 21 days.

Greylisting is effective because many mass e-mail tools utilized by spammers are not set up to handle temporary bounces (or any bounces, for that matter; they will never bother to retry a failed delivery), so the spam is never delivered.

Does greylisting stop all spam?

No system can be 100% effective in stopping spam. Implementation of greylisting has been proven to significantly reduce the amount of spam received.

Will greylisting block valid email messages?

Greylisting will eventually allow all mail servers that follow internet standards for resending messages to process normally. However, some legitimate mail systems don't follow these standards.

Does greylisting replace spam or virus filtering?

No. Greylisting is another level of protection against unwanted email, but it does not replace other spam filtering or anti-virus scanning. Spam Assassin will still operate on Expat Email servers for email that does get through the greylisting process. Other FAQs cover how this can be configured and trained.

Will there be long delays in delivery of email to me?

Delays in email delivery will depend on the settings of the sending mail server. E-mail affected by greylisting will be delayed a minimum of 10 seconds. This is the delay interval required in order to prevent immediate redelivery by already-connected SPAM servers. The message may be redelivered without challenge by the servers for up to 12 hours. After 12 hours, the original record of the message is destroyed and the challenge/redelivery process must begin again.

Internet specifications suggest that messages temporarily refused should be redelivered within 4 hours, and most servers are configured to retry in far less time - often on the order of 5 minutes. The specific delay will depend on the configuration of the sender's e-mail servers

How does greylisting help me?

Greylisting should block a large percentage of spam. You should see less spam in your Inbox. Most email that is processed by the Expat Email mail system is spam. Greylisting will reduce the amount of unwanted email that comes into the Expat Email mail system and therefore should reduce the overall system load, thus improving performance.

Can I turn off greylisting?

No. Greylisting is implemented at the mail server level.

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