Greylisting

The greylisting is a very simple technique antipourriel which consists in rejecting a message temporarily, by emission of a code of temporary refusal to the transmitting waiter (MTA). In the majority of the cases, the transmitting waiters reforward the email after a few minutes. The majority of the waiters emitting of the Pourriel S would not take this trouble.

Operation

For each received email one creates a triplet identified by address IP of the transmitting waiter, the address email of the shipper and the address email of the recipient. If the triplet appears for the first time, the mail server returns a code 4xx (temporary refusal) to the waiter distant smtp. If this waiter is a genuine waiter smtp, the email will be reforwarded later on. If the triplet reappears after a certain time (skeletal, to envisage between 15 minutes and half an hour) the message is accepted and the triplet added to a list of confidence (" whitelist"). If the email is reforwarded before this time, he is again temporarily refused. After a certain deadline (4 or 5 hours), triplets of the " greylist" are removed. Moreover, one rebootstrapping of the lists of confidence is recommended periodically (between 1 week and 1 month).

Implementation

The solution of protection of the transport ALTOSPAM uses Greylisting.

External bonds

www.greylisting.org
the greylisting, French translation of the text of Ewan Harris

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