Delaying is a new method of blocking significant amounts of spam at the mailserver level, but without resorting to heavyweight statistical analysis or other heuristical approaches. This method is also called "Greylisting".
Delaying/greylisting is an extremely powerful ASSP feature to fight spam; false positive are near or exactly 0. By default there is an embargo time of 5 minutes (default)
What does it means? How does work the DELAYING filter?
As explained also on the ASSP Deluxe Cpanel web interface (HELP button) Delaying is a method of blocking significant amounts of spam at the mailserver level, but without resorting to heavyweight statistical analysis or other heuristical approaches .This method is also called "Greylisting".
Delaying works on the idea that a correctly configured SMTP server will always attempt re-delivery of an email message if it gets a soft failure.
How does it work exactly?
When someone send an email to our server (and you or your client have the delaying filter enabled), ASSP will return a 451 error (soft failure) which requests deliverly again later. If the sending mail server is correctly configured it will reattempt deliver in X number of minutes. (it depends upon his configuration). If the sender mail server waits and redelivers, the triplet (email address, domain, IP) gets whitelisted (delaying whitelist) and you'll receive the email .
When will you receive the email?
If the mail server is configured correctly you should receive the email after min 5 minutes (default embargo time) and max 28 hours (default wait time). If the Spammer mailserver doesn't reattempt the deliver (and the spammers usually do not reattempt the deliver) the email will be rejected after the wait time (28 hours) and you'll never receive the spam message.
May I lose some valid email?
Only if the sender (mailserver sender) is not configured to reattempt the deliver the email will be rejected. If the client can see some valid email on his delaying Log page he can still whitelist the email using the REPORT button.
By RFC, all mailservers have to retry the delivery.
Please read also http://apps.sourceforge.net/mediawiki/assp/ for other info.
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