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William Edwards

2019-Dec-27 14:02 UTC

Dovecot proxy: authentication best practices

Hi!

I have a few questions regarding Dovecot proxy:

1.
1.1 If I understand correctly, setting 'nopassword' in the proxy passdb
file, authentication is completely up to the destination host. Setting
'nopassword' in no way means the proxy becomes an open relay. Is this
correct?
1.2 Are there any security implications when using 'nopassword' on the
proxy?

2.
2.1 I would like to avoid having to store all users in a passdb file on the
proxy. I would much rather specify a domain for which Dovecot proxy will route
all users to a specific host. Is there a way to let Dovecot proxy route to a
destination host based on domain, so individual users don't have to be
specified in the proxy passdb?
2.2 Is it correct that userdb does not have any effect on proxying and it can be
left out of the config? Source:
https://dovecot.org/pipermail/dovecot/2013-October/093138.html (point 2)


Met vriendelijke groeten,

William Edwards
T. 040 - 711 44 96
E. wedwards at cyberfusion.nl




?

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Aki Tuomi

2019-Dec-27 16:42 UTC

head link

Dovecot proxy: authentication best practices

<!doctype html>
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    On 27/12/2019 16:02 William Edwards <wedwards@cyberfusion.nl> wrote:
   </div>
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    <br>
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   <div style="font-size: 13px;" dir="auto"
class="iw_mail">
    <div>
     Hi!
    </div>
    <div>
     <br>
    </div>
    <div>
     I have a few questions regarding Dovecot proxy:
    </div>
    <div>
     <br>
    </div>
    <div>
     1.
    </div>
    <div>
     1.1 If I understand correctly, setting 'nopassword' in the proxy
passdb file, authentication is completely up to the destination host. Setting
'nopassword' in no way means the proxy becomes an open relay. Is this
correct?
    </div>
   </div>
  </blockquote>
  <div>
   <br>
  </div>
  <div>
   You still control where it proxies to.
  </div>
  <blockquote type="cite">
   <div style="font-size: 13px;" dir="auto"
class="iw_mail">
    <div>
     1.2 Are there any security implications when using 'nopassword' on
the proxy?
    </div>
    <div></div>
   </div>
  </blockquote>
  <div>
   <br>
  </div>
  <div>
   As long as its really a proxy, probably no.
  </div>
  <blockquote type="cite">
   <div style="font-size: 13px;" dir="auto"
class="iw_mail">
    <div>
     2.
    </div>
    <div>
     2.1 I would like to avoid having to store all users in a passdb file on the
proxy. I would much rather specify a domain for which Dovecot proxy will route
all users to a specific host. Is there a way to let Dovecot proxy route to a
destination host based on domain, so individual users don't have to be
specified in the proxy passdb?
    </div>
    <div>
     2.2 Is it correct that userdb does not have any effect on proxying and it
can be left out of the config? Source:
https://dovecot.org/pipermail/dovecot/2013-October/093138.html (point 2)
    </div>
   </div>
  </blockquote>
  <div>
   userdb is ignored on proxies. For your usecase try following
  </div>
  <div>
   <br>
  </div>
  <div>
   passdb {
  </div>
  <div>
     driver = passwd-file
  </div>
  <div>
     args = username_format=%Ld /etc/dovecot/domains.passwd
  </div>
  <div>
   }
  </div>
  <div>
   <br>
  </div>
  <div>
   and into domains.passwd
  </div>
  <div>
   <br>
  </div>
  <div>
   domain.com::::::: nopassword proxy host=host1
  </div>
  <div>
   <br>
  </div>
  <div>
   colon count might be wrong
  </div>
  <blockquote type="cite">
   <div style="font-size: 13px;" dir="auto"
class="iw_mail">
    <div class="iw-signature">
     <div></div>
     <div>
      Met vriendelijke groeten,
     </div>
     <div>
      <br>
     </div>
     <div>
      William Edwards
     </div>T. 040 - 711 44 96
     <div>
      E. wedwards@cyberfusion.nl
     </div>
    </div>
   </div>
  </blockquote>
  <div class="io-ox-signature">
   <pre>---
Aki Tuomi</pre>
  </div> 
 </body>
</html>

William Edwards

2019-Dec-28 10:18 UTC

head link

Dovecot proxy: authentication best practices

Hi Aki,
> 1.1 If I understand correctly, setting 'nopassword' in the proxy
passdb file, authentication is completely up to the destination host. Setting
'nopassword' in no way means the proxy becomes an open relay. Is this
correct?
> You still control where it proxies to.
> 1.2 Are there any security implications when using 'nopassword' on
the proxy?
> As long as its really a proxy, probably no.
Ok, so assuming proper authentication is configured on the destination host, the
answer to 1.1 is 'yes' and the answer to 1.2 is 'no'.
> userdb is ignored on proxies. For your usecase try following
> and into domains.passwd
Ah, yes, of course. I forgot Dovecot supports multiple passdb backends. I have
added the domains.passwd backend as a fallback.

Thanks!

Met vriendelijke groeten,

William Edwards
T. 040 - 711 44 96
E. wedwards at cyberfusion.nl

?
----- Original Message -----
From: Aki Tuomi (aki.tuomi at open-xchange.com)
Date: 12/27/19 17:42
To: William Edwards (wedwards at cyberfusion.nl), dovecot (dovecot at
dovecot.org)
Subject: Re: Dovecot proxy: authentication best practices

On 27/12/2019 16:02 William Edwards <wedwards at cyberfusion.nl> wrote:

Hi!

I have a few questions regarding Dovecot proxy:

1.
1.1 If I understand correctly, setting 'nopassword' in the proxy passdb
file, authentication is completely up to the destination host. Setting
'nopassword' in no way means the proxy becomes an open relay. Is this
correct?

You still control where it proxies to.

1.2 Are there any security implications when using 'nopassword' on the
proxy?

As long as its really a proxy, probably no.

2.
2.1 I would like to avoid having to store all users in a passdb file on the
proxy. I would much rather specify a domain for which Dovecot proxy will route
all users to a specific host. Is there a way to let Dovecot proxy route to a
destination host based on domain, so individual users don't have to be
specified in the proxy passdb?
2.2 Is it correct that userdb does not have any effect on proxying and it can be
left out of the config? Source:
https://dovecot.org/pipermail/dovecot/2013-October/093138.html (point 2)

userdb is ignored on proxies. For your usecase try following

passdb {
? driver = passwd-file
? args = username_format=%Ld /etc/dovecot/domains.passwd
}

and into domains.passwd

domain.com::::::: nopassword proxy host=host1

colon count might be wrong

Met vriendelijke groeten,

William Edwards
T. 040 - 711 44 96
E. wedwards at cyberfusion.nl

---
Aki Tuomi

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