Mailing lists and GREY LISTING
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.