Reject emails to nonexistent addresses?

[Steve Swaney]

> -----Original Message-----
> From: MailScanner mailing list [mailto:MAILSCANNER at JISCMAIL.AC.UK] On
> Behalf Of Martin Hepworth
> Sent: Friday, January 21, 2005 4:06 AM
> To: MAILSCANNER at JISCMAIL.AC.UK
> Subject: Re: Reject emails to nonexistent addresses?
>
> I note that verizon are a milter-ahead style sender verification and its
> causing quite a few problems..

This looks like milter-sender not milter-ahead. Milter-sender attempts to
use various tactics to verify the address of the sender exists and is in
good standing before accepting an email. I quote from the milter-sender web
site:

Start quote "
Sendmail milter (Sendmail's term for a mail filter) attempts to address a
small subset of the problem by verifying that the sender's email address is
in good standing by performing an SMTP callback to the MX server responsible
for the sender's domain. This milter is not intended to be a complete
solution to spam and so it should be used in conjunction with other tools
such as DNS blacklists and content filters.

To be in good standing, the MX server of the sender must be reachable and
willing to accept email for the sender from the Delivery Status Notification
(DSN) address, which is the null address <> used for error reporting. This
particular requirement is similar to using the RFC-Ignorant DSN Blacklist.

During the callback, any failure in establishing an SMTP connection such as
no DNS entry or the primary MX server is unreachable, or during the SMTP
dialogue such as not accepting the DSN, user unknown, or mail box is full,
etc. will result in the incoming mail in question being rejected. In the
case of a temporary error during the SMTP dialogue with the sender's MX
server, milter-sender will reject the current message with a temporary error
code, which the sender is then free to retry again later. DNS lookup and
connection problems are treated as temporary errors.

The milter will check secondary MX mail servers, though this does weaken the
test somewhat. In order to compensate and without having to resort to
sending a challenge message, a grey listing technique is applied to servers
that appear to blindly accept everything.
"End quote

This is quite a bit different than milter-ahead which we use on our gateways
to verify that the recipient exists on our backend mailhub.

We do not use milter-ahead to reject email. I can see too many possibilities
for error and have not tested.

Steve

Steve Swaney
President
Fortress Systems Ltd.
www.fsl.com
steve.swaney at fsl.com




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