From: Adam Gibson
Date: 2005-02-18 10:23:50 -0500
Subject: Re: user account fishing
More information..: http://www.milter.info/#Support
I have run across a problem where a mail server was doing something
similar to combat spam which caused us to become deadlocked with each
other and not be able to send email to their domain because they blocked us.
From what their email admin told me they apparently put some bogus
emails on their website for spam email harvesters to find. The
anti-spam software they use waits for a mail server to try and send an
email to that trap email address and temporarily sets a block on that
sending server. I think you can see where this is going...
A spammer sends an email to us with a from address of a random email
from their harvested list which just happens to be one of the emails
that the company put on their website. Milter-sender sees the from
address and tries to do a verification of the email address against
their email server. Their email server sees the rcpt to: with the trap
email address and blocks our servers for awhile... Hours later when we
try to resend it we get the same thing over again.
Meanwhile any emails that we need to send to that companies domain just
get rejected by their server because of the spam email that is trying to
get sent to our domain.
I had to manually contact their email admin to get all this straightened
out but eventually we both setup a whitelist to bypass the spam checks
for each others mail servers.
I sure hope this is not something that will catch on because it could
cause major problems with milter-sender. Has anyone else seen this type
of spam protection on mail server before?
Aaron Berg wrote:
> One idea might be to just keep a log of valid email addresses in a
> specified database. Then just autoblacklist ip's for some period of time
> after they have tried too many non-valid addresses. But it seems like
> this would be more work then is needed. Could the milter just parse
> passwd and virtusertable for valid email addresses just like sendmail
> does? Where there is a will there is a way.
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