Difference between revisions of "Greylisting"

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* [http://slashdot.org/articles/03/06/20/168203.shtml?tid=111&tid=126 Slashdot | The Next Step in Fighting Spam: Greylisting]
 
* [http://slashdot.org/articles/03/06/20/168203.shtml?tid=111&tid=126 Slashdot | The Next Step in Fighting Spam: Greylisting]
  
* [http://greylisting.org/articles/whitepaper.shtml The Next Step in the Spam Control War: Greylisting]
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* [http://www.ietf.org/rfc/rfc2821.txt Internet Engineering Task Force, RFC 2821]
  
* [http://www.ietf.org/rfc/rfc2821.txt RFC 2821]
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* [http://greylisting.org/articles/whitepaper.shtml The Next Step in the Spam Control War: Greylisting]

Revision as of 15:46, 30 November 2006

You may have received an error similar to this when attempting to send an email:

Recipient address rejected: Greylisted for 115 seconds, see http://supranet.net/greylist/

Please read on!

What is Greylisting?

Greylisting is a term used for a process that reduces the amount of unsolicited e-mail (SPAM) delivered to e-mail addresses by capitalizing on SPAMmers' reluctance to configure their mail servers according to internet standards. With greylisting, our servers maintain a record of three pieces of information when an e-mail is received:


  1. The IP address of the machine sending the e-mail.
  2. The e-mail address of the person sending the e-mail.
  3. The e-mail address to which the e-mail is being delivered.


This set of information is captured and recorded on the servers, and communication with the sender's server is terminated with an error code before the content of the e-mail message is received. Our servers reply to the sending server to say essentially "Sorry, we're too busy right now. Please try again to send this e-mail later." The error message (called a "400-level error") is specifically "temporary" and properly configured mail servers will queue the message and retry after some period of time.

Once a period of 3 minutes passes, the message is then passed through without this delay. From that point on, anytime a message with the matching information is received, it is delivered immediately.

More Information