[Dovecot] what best for anti-spam filter?

[Stan Hoeppner]

On 7/24/2012 7:13 AM, Morten Stevens wrote:

> Jul 24 12:27:32 mx1 sendmail[31933]: q6OARUOM031928:
> to=<dovecot at dovecot.org>, delay=00:00:02, xdelay=00:00:01, mailer=esmtp,
> pri=152317, relay=dovecot.org. [193.210.130.67], dsn=2.0.0, stat=Sent
> (Ok: queued as 35AF81AE8359)
> Jul 24 12:28:32 mx1 sendmail[31933]: q6OARUOM031928:
> to=<manu at netbsd.org>, delay=00:01:02, xdelay=00:01:00, mailer=esmtp,
> pri=152317, relay=mail.netbsd.org. [149.20.53.66], dsn=4.0.0,
> stat=Deferred: Connection timed out with mail.netbsd.org.
> Jul 24 12:42:57 mx1 sendmail[32292]: q6OARUOM031928:
> to=<manu at netbsd.org>, delay=00:15:27, xdelay=00:01:00, mailer=esmtp,
> pri=242317, relay=mail.netbsd.org. [149.20.53.66], dsn=4.0.0,
> stat=Deferred: Connection timed out with mail.netbsd.org.
> Jul 24 12:50:53 mx1 sendmail[32518]: q6OARUOM031928:
> to=<manu at netbsd.org>, delay=00:23:23, xdelay=00:00:02, mailer=esmtp,
> pri=332317, relay=mail.netbsd.org. [149.20.53.66], dsn=4.7.1,
> stat=Deferred: 450 4.7.1 <manu at netbsd.org>: Recipient address rejected:
> Greylisting in action, please try later
> Jul 24 12:58:41 mx1 sendmail[312]: q6OARUOM031928: to=<manu at netbsd.org>,
> delay=00:31:11, xdelay=00:00:02, mailer=esmtp, pri=422317,
> relay=mail.netbsd.org. [149.20.53.66], dsn=4.7.1, stat=Deferred: 450
> 4.7.1 <manu at netbsd.org>: Recipient address rejected: Greylisting in
> action, please try later
> Jul 24 13:42:21 mx1 sendmail[1461]: q6OARUOM031928:
> to=<manu at netbsd.org>, delay=01:14:51, xdelay=00:00:01, mailer=esmtp,
> pri=512317, relay=mail.netbsd.org. [149.20.53.66], dsn=4.7.1,
> stat=Deferred: 450 4.7.1 <manu at netbsd.org>: Recipient address rejected:
> Greylisting in action, please try later
> Jul 24 13:50:53 mx1 sendmail[1672]: q6OARUOM031928:
> to=<manu at netbsd.org>, delay=01:23:23, xdelay=00:00:02, mailer=esmtp,
> pri=602317, relay=mail.netbsd.org. [149.20.53.66], dsn=4.7.1,
> stat=Deferred: 450 4.7.1 <manu at netbsd.org>: Recipient address rejected:
> Greylisting in action, please try later
> 
> This is exactly the reason why greylisting is bad.

I have yet to hear of a bot that retries.  Thus, there's not reason to
set a wait period more than a few seconds, causing the situation above.

That said, there is another use of greylisting not related to bots,
which is delaying clients long periods of time in hopes that snowshoe
servers will get listed by one's fav dnsbl.  Though this isn't very
effective against snowshoe.  Which is why few use it for this purpose.

-- 
Stan