Reverse E-Mail Blockage.....

Dave Ihnat dihnat at
Mon Dec 30 05:24:30 UTC 2013

On Sun, Dec 29, 2013 at 07:53:53PM -0800, Joe Zeff wrote:
> I have a friend who's email service sporadically bounces my email.
> Why?  Because I own my own domain, I use my hosting company's email
> servers instead of my ISP's and a small number of their customers
> are spammers.  Whenever their spam gets above a certain threshold,
> her ISP blocks any email access from those servers, and cuts us off.

It's called a shared server, and is one of the greatest complaints I get
from my clients.  Essentially, ISPs in the past have often used the same
server to deliver E-Mail for multiple--often hundreds--of hosted clients.
As you've discovered, one bad neighbor will cause the shared server IP to
be blocked.  Given the current state of SMTP protocol and the ability to
forge anything except the IP, there's nothing to do about this--there
is no better way to identify offenders.

The solution is to get a private IP from your ISP if they're hosting your
mail server.  It usually costs a few dollars to do so, but guarantees
that your IP isn't tainted by others on the same server.  (There are some
RBLs that reject by IP blocks, but most have fallen by the wayside over

> This is why I dislike blacklists: they're just about guaranteed to
> produce at least 99% false positives because they're just an
> exercise in throwing the baby out with the bath water.

Most RBLs have options to request delisting, and even without that will
usually delist after a few hours unless there's a repeat report.  Most ISPs
have an interest in clearing their servers from RBLs, and if notified that
one or more of their IP addresses are blocked will take steps to identify
and clear up shared host problems.

Yes, there are some RBLs that are "bad eggs".  If they regularly provide
bad rejections, mailhosts stop using them.  The worst problem is from
the major ISPs themselves--e.g., Yahoo, and most particularly Hotmail.
They maintain their own internal blacklists, don't give tools for
identification, and have horrible removal request/response policies.

	Dave Ihnat
	dihnat at

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