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Mailing lists and GREY LISTING

2011-10-12 14:22:33

On 11.10.2011 19:45, Steve Atkins wrote:

For classic greylisting that's all quite true (he whole point of greylisting is 
the assumption that bad actors will not retry, while good actors will). 
Greylisting does damage some forms of email, though - discussion lists, where 
emails are delayed by seemingly arbitrary amounts, breaking up the flow of 
conversation are one - but I can't think of any good way to mitigate that 
damage other than telling servers not to use greylisting or telling clients to 
retry quickly, neither of which seems like a good idea.

Discussion list have often the property, that only a limited amount of email addresses can post to the list (if the mail is spread over the list depends on SMTP env from:/MIME Redirect-...:, From:, Sender:) and all other emails are not distributed over the list. So when an email is evaluated for spaminess, apart from the usual criteria, the env from:/MIME From:, Sender, Redirect-(From,Sender): have to be correct. To my knowledge, spammers writing to mailing list do not have information what to put as From: in order to get the mail delivered. Spam over mailing lists arrives (most often) due to hacked mailbox-passwords and this problem is not avoided by greylisting. For discussion lists I suggest to disable greylisting and instead permanently reject the emails (at SMTP level based on the MIME-Headers), which would not be distributed over the list. Rejecting mails (for mailing lists) at SMTP level is anyway a godo idea, is it leads to decreasing the amount of bounces.

I know this mailing list is about SMTP, but when it comes to greylisting settings, apart from exposing them over SMTP, it would be nice, if every recipient has the possibility to tell his SMTP server the recipient's preferred greylisting - settings (if IP/From or IP/From/To shall be proceeded for this recipient, preferred parameters for time retries). This could be achieved by Sieve extension, that is evaluated at SMTP-Time-- the recipient stores there his greylisting preferences, and the server considers them when it proceeds a message for that recipient.

Със здраве

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