Greylist

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Another method of stopping spam

Nowadays most spam is sent from infected home PCs in private homes. The spambots running on a PC do not have any logic for resending a failed message, these applications appear to adopt the "fire-and-forget" methodology. A decent mail server however, will try to deliver a message for at least 3 days.

You are probably reading this page since you got this error message:
421-Nice to meet you - please try again in 10 minutes
421-For more information see: http://tjinfo.uib.no/greylist.html
421 or contact postmaster@uib.no

Mail is transfered between mail servers using the protocol SMTP, defined in RFC2821. During delivery the receiving server will respond with three-digit codes:

  • 2xx means OK
  • 4xx notifies that a temporary error has occured. The sending server should retry delivering the message.
  • 5xx is a permanent rejection, ie "user unknown". The sending server should give up on the message, reporting the failed delivery to the sender.


While a real mail server will retry after the reception of a 421-message, spammers will not!

Current configuration at the University of Bergen will reject a message the first time it is seen. After 3 minutes a message from the same sender and host to a local user in Bergen will be accepted. After this reception all further mails will be accepted with no further delay.

If you are receiving this error while sending mail to the University of Bergen your mail server is broken and you should contact your support personal demanding the server to be upgraded so that it is conforming to the Internet standards. When a 421 reply is received, your server should requeue the mail and retry after some time. At the University of Bergen a message will be retried for five days untill it is returned to the sender.

If you still have problems reaching students or employed at the University of Bergen, your mail to postmaster@uib.no will be accepted. We will respond to such mails by whitelisting your server so that this test will not be run on your further deliveries.

For more information about greylisting, please look at puremagic.