What is greylisting?
A way to block spam. Greylisting is based entirely on the behavior of the server sending email. It doesn't consider content at all. Greylisting looks at the sender address, the recipient address and the sending IP address. If these haven't been seen together before, delivery is quarantined and will only be sent if the sender attempts to send the message again within a configurable time period. Once a sender is recognized as legitimate, the address is removed from the greylist and future messages will pass through immediately. This process will eliminate most spam while allowing desired email to come through.
Greylisting is complimentary to other spam filtering techniques. There is no special configuration requirements by the end user and no resource drain on the end user's computer.
The name greylist comes from being between a blacklist and a whitelist. A blacklist is email addresses or domain names that are known spam sources. A whitelist is just the opposite. It is email addresses or domain names which will be allowed to be sent through to the recipient.
- Blocks spam
- Allows desired email to come through
- Requires no end user configuration
- Causes no drain on end user's equipment
Is there a downside?
Graylisting can cause a delay in the recipt of initial messages. It also doesn't notify senders of legitimate email that has been falsely identified as spam.
Helpful links for more information:
BlueChannel.com Spam Service
Greylisting - Wikipedia, the free encyclopedia
Greylisting.org - a great weapon against spammers
Spam Links - greylisting
Greylisting: The Next Step in the Spam Control War
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