[attribution of quotes reconstructed]
On Sat, Aug 17, 2013 at 12:54:44AM -0700, Grant wrote:
Noel:
> > However, I wonder why you don't have any dns blacklists such
> > as zen.spamhaus.org defined there. The ability of postscreen
> > to reject known bad sites without using precious smtpd
> > processes is one of its key features.
Grant:
> > I would just rather have a false negative than a false positive.
> > I get a pretty small amount of spam at this point so I don't
> > think reducing it further is worth increasing the chances of a
> > false positive.
Charles:
> > From what (little) I know about how postscreen works, rejecting
> > the known bad sites doesn't really have any (substantive) chance
> > of false positives, but it provides much more than just
> > protection from spam - it protects you from the botnets/zombies
> > hammering your server needlessly.
>
> Do you mean there aren't any legitimate servers listed in
> zen.spamhaus.org?
Zen is a composite list, and indeed it is intended to be safe for
widespread use.
SBL (Spamhaus Block List) lists IP addresses which are known to be
under the control of spammers.
XBL (Exploits Block List) lists IP addresses which are actively
spewing bot spam. Legitimate servers are occasionally listed in XBL,
because they meet that condition. Some short time after they stop
their abuse, they are delisted. Typically this is less than a day.
PBL (Policy Block List) lists IP addresses which, according to the
netblock owners, should not normally be sending legitimate email.
Exceptions can be made for hosts with custom PTR upon request. Many
colocation providers submit their networks for PBL, but removal is
easy.
> When I switched servers a while back, the new IP
> I received was listed on several blacklists and it was a hassle
> to get them removed.
Far better that you go through that step than the Internet be exposed
to more spam. Anyway, did you notice how bad your deliverability was
during the time of your PBL listing? That's how it is. Lots of
Internet sites use Zen for blocking.
There is safety in numbers. Any Zen-listed site which is wanting to
deliver mail to you is also having problems getting mail to the rest
of the Internet. They simply must address the problem[s] that caused
the listing.
All that said, to address a point from Charles above, sure, it is
possible for an over-eager person to make a postscreen which will
block non-spam. Here's my example postscreen configuration which is
intended to be safe and reasonable for most uses:
http://rob0.nodns4.us/postscreen.html
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