[Greylist-users] Why and how often greylisting fails against ordinal servers?

[Akihiro KAYAMA]

Hi all.

I'm trying greylisting for a couple of weeks with postfix
greylist.pl(fully customized) and it works very well. 

But recently, I found a server which do not tend to retry respond to
temporary failure(450). The problem is that it seemed to be a ordinal
Sendmail(8.11.7/3.7W) server which ordinal company runs for
transferring ordinal business mail. "Ordinal" means, the server is not
a mailing list server or proxy server, not an ISP, not a
unsophisticated special MTA, not a mail clustering server, and they
are not a spammer, not a IT-related company which operate huge amount
of mail, etc.

I think they run Sendmail with no retrying configuration, but I don't
know why. Anyway, because it causes unwanted critical false-positive,
I want to know why they do so intentionally or unintentionally, and
estimate how much (ordinal) servers run under such a temporary error
intolerant (something special or miss) configuration.

Do you have any ideas and/or similar experiences?
Thanks.

-- kayama