Dovecot Proxy

[Thoralf Rickert-Wendt]

Hi Philon,

now, it's time for "Mahlzeit" ;-)

Sorry, that I read the wiki1 instead of wiki2. I thought the 1 means 
that it is server one of ... my fault. Also not reading the first line 
above the menu. My focus was really on the content. ;-)

Also my problem with the doc of Dovecot2 proxy is, that the document 
https://doc.dovecot.org/configuration_manual/authentication/proxies/ has 
less details for a domain only example. That works as in the Dovecot1 
doc, but it isn't documented anymore. Also the location under 
"authentication" chapter in the Wiki didn't tell me, that this is the 
"new Dovecot proxy documentation". I thought, this was only related to 
authentication issues. I would recommend to either restructure the 
wiki2, that it makes it more clear to the user or make some notes on 
https://doc.dovecot.org/admin_manual/dovecot_proxy/ and link to the 
passdb setting on 
https://doc.dovecot.org/configuration_manual/forwarding_parameters/ and 
https://doc.dovecot.org/configuration_manual/authentication/proxies/. 
Maybe there are other documents related to Proxy too, like the SNI 
settings etc. But maybe I'm the only one on the planet, that tries to 
use that. It feels a little bit like that.

The Director would be interesting, if all the mailservers in the backend 
would know each other. But thats not the case. Mailserver A and 
Mailserver B are hosting complete different domains with a complete 
different user list and complete different user admins, etc. Also 
mailcow doesnt enabled the director. So it will not help much. But it 
could be interesting, if I have multiple proxies.

Yes, the submission service inside Dovecot is there. And I tried to 
avoid to install multiple "programs" and if there is one "program" that 
handles it all, why don't use it. And I'd like to quote the first line 
of the Dovecot proxy doc: "Dovecot supports proxying IMAP, POP3, 
Submission Server 
<https://doc.dovecot.org/admin_manual/submission_server/#submission-server>, 
LMTP Server 
<https://doc.dovecot.org/configuration_manual/protocols/lmtp_server/#lmtp-server>, 
and Pigeonhole ManageSieve Server 
<https://doc.dovecot.org/admin_manual/pigeonhole_managesieve_server/#pigeonhole-managesieve-server> 
connections to other hosts.".

Also I tried to open the Dovecot authentication mechanism for postfix 
(for submission) with


service auth {
   user = root
   unix_listener /var/spool/postfix/private/auth {
     group = postfix
     mode = 0660
     user = postfix
   }
}

And on Postfix part with

smtpd_sasl_auth_enabled = yes
smtpd_sasl_type = dovecot
smtpd_sasl_path = private/auth

But the postfix login is always accepted (even with wrong passwords) and 
after I start to write a Mail the connection get lost after RCPT 
command. There is another problem. Before I infestigate it, I would try 
my luck with Dovecot. It is already asking the correct backend 
submission server but with SSL on a non-SSL port.

So - someone included the Submission protocol in Dovecot and someone 
wrote, that the submission could be proxied - but - its not completly 
documented or "it doesn't work" within a SSL environment. I searched for 
a simple example, where IMAP and POP3 are proxied via SSL and Submission 
too (which would mean, that Dovecot submission listens on 465) or via 
STARTTLS on 587 and redirecting it also to STARTTLS/587. But I didn't 
find anything. Also the submission documentation doesnt help, because I 
cant see any line of configuration file in it.

Ok, but first - lunchtime.

bye
Thoralf

Am 01.09.20 um 09:43 schrieb Philon:
> Hi Thoralf,
>
> I’d say first of all you should read the current docs for 2.x not the archived stuff. —> https://wiki2.dovecot.org/ - (It’s even mentioned in bold in the header)
>
> Then to front multiple backends perhaps you want to take a look at Dovecot Director. —> https://wiki2.dovecot.org/Director
>
> About SMTP I’m not sure why you would want to rely on Dovecot for that. I only do Postfix with Dovecot as auth backend so they can share passdb access. When you have 465 set up it is no big deal to also enable 587 in Postfixs master.cf.
>
> If you want to keep Dovecot for Submission you can check the latest docs for Dovecot submission service: https://doc.dovecot.org/admin_manual/submission_server/. It has a relay server option with port. Also settings for STARTTLS etcpp can be found there.
>
>
> Mahlzeit!
>
> Philon
>
>> On 31 Aug 2020, at 11:33, Thoralf Rickert-Wendt <trw at acoby.de> wrote:
>>
>> Hello everyone,
>>
>> it's my first post here on this mailing list and I hope, I make it right.
>>
>> I posted a question on https://serverfault.com/questions/1031441/dovecot-as-proxy-with-submission and nobody was able to answer it. So I decided to push that question here (I'm talking about any new dovecot version and I've tested it with 2.3.4.1 (f79e8e7e4)).
>>
>> I try to run a dovecot proxy in front of a big number of mail servers (serving SMTP-in, submission, IMAP, POP3, Sieve). I need that proxy, because I run out of IPv4 addresses. Of course I use IPv6 too, but many customers still have problems with there providers and they really don't want to share their mails on a "shared-mailserver". I planed to use Dovecot for IMAPS, POP3S, SMTP-submission(465) and postfix for the rest. If I find a solution for sieve, I would try that too, but that is very optional.
>>
>> With the documentation https://wiki1.dovecot.org/HowTo/ImapProxy (which is really old and should be updated) and some other ascii docs (from an Apple mirror somewhere deep in the web) I was able to build a IMAP/POP3 proxy that forwards requests from outside to a specific backend using SSL (993,995). That works - I think.You can find the config on the serverfault page.
>>
>> In general - all known domains in backend are using SSL and the passdb forwards all requests to the backend via SSL. So - I understand:||
>>
>> |password_query =
>>    SELECT
>>      NULL AS password,
>>      NULL AS destuser,
>>      host,
>>      'Y' AS nologin,
>>      'Y' AS nodelay,
>>      'Y' AS nopassword,
>>      'Y' AS proxy,
>>      'any-cert' AS `ssl`
>>    FROM
>>      proxy_domain
>>    WHERE
>>      domain = '%d' |
>>
>> But that is only 50% of the show. The rest ist submission (and maybe sieve). Practically the submission implementation in dovecot works too. But because dovecot by default only opens port 587 (starttls), my passdb setting has a problem.
>>
>> When I try to use that port Dovecot tries to use SSL on the backend/587 too - but that is wrong (it should either use 465 or should try to use starttls).
>>
>> So, I have the following options.
>>
>> - find a way to configure dovecot-proxy to listen on 465 with SSL for submission service and hope that it uses the same port
>>    - but I didn't find any documentation for that and need help
>>
>> - find a way to configure dovecot-proxy/passdb to return starttls=y when dovecot-submission is used (use a different passdb)
>>    - but I didn't find any documentation for that and I'm not sure, if this worls on service/protocol level
>>
>> - find a way to configure the passdb answer based on the used port/protocol. But I only know the parameter %u, %d and %p.
>>    - so it would be nice to find a way to also select the protocol (if already developed)
>>
>> - find a way to make a patch in dovecot (which isn't easy for me, because I don't really know the code)
>>
>> Has somebody an idea, how I can configure the dovecot-proxy in that way.
>>
>> bye
>> Thoralf
>>
>>
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