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<pre>On 15 Jul 2019, at 18:11, Trever L. Adams via dovecot <<a href="https://dovecot.org/mailman/listinfo/dovecot">dovecot at dovecot.org</a>> wrote:
><i> So, one of the problems I am seeing is that people are trying to fake
</i>><i> users into revealing information by sending from an outside domain but
</i>><i> with an internal reply to address and claiming to be administration, IT
</i>><i> or what not.
</i>
You should not accept external mail claiming to be from your domain unless that mail comes via authenticated submission. But if the reply to is going to an internal address…
I’m puzzled by exactly what you mean here. Are you saying that users on your system are trying to phish other users on your system?
><i> I can set up something that will reject if from is outside the domain by
</i>><i> reply to is internal. The problem is in some setups, there are fetchmail
</i>><i> setups. I do not want to reject these with a message. Which is what I am
</i>><i> currently doing for the others. Maybe I should discard them all without
</i>><i> rejecting.
</i>
I haven’t used fetch mail in many many years, so I can’t answer anything specifically about it, but if you use it to allow external senders to send mail via your system in a way that is not authenticated then you should not do that.
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<p>I do NOT allow email claiming to be from my domains. The problem
is "forgery" of Reply-To headers. It isn't really forgery as far
as I know there is now method to check this anywhere. People are
allowed to put what they want there. The setups in question do NOT
allow unauthenticated submission with a FROM from the internal
domain.</p>
<p>I have erased the email in question, so I cannot give an exact
example but it is something like this:</p>
<p>From: <a class="moz-txt-link-abbreviated" href="mailto:something@devcubesomething.org">something@devcubesomething.org</a> (I remember cube and dev in
the domain)<br>
</p>
<p>To: trever@thedomain (yes it was sent to me, thankfully not one
of the other users)</p>
<p>Reply-To: info@thedomain (yes, stupid account to use, but that
was it)</p>
<p>Subject: Your account will be deleted/deactivated</p>
<p>Some nonsense about having failed to follow directions and if I
don't click the link below, the account would be deleted. It was
NOT talking about an account on another system, but the email
account itself.</p>
<p><br>
</p>
<p>So, as you see, it is coming from an outside domain. As the sieve
code showed, I am testing for where reply-to claims to be for
internal domain, but the from is NOT from it. This email was a
good example of that.<br>
</p>
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