Dovecot submission announces CHUNKING but backend Postfix does not support it

[Michael Goth]

On 09/20/2018 10:24 PM, Stephan Bosch wrote:
> 
> 
> Op 20/09/2018 om 13:39 schreef Michael Goth:
>> On 09/20/2018 12:56 PM, Robert Schetterer wrote:
>>> Am 20.09.2018 um 11:04 schrieb Michael Goth:
>>>> Hello,
>>>>
>>>> I'm setting up Dovecot 2.3.2.1 as a submission proxy to a Postfix 
>>>> backend server. Dovecot announces CHUNKING, but the Postfix backend 
>>>> does not support (or announce) it.
>>>>
>>>> HELO from Postfix:
>>>>
>>>>    220 backend.mydomain.com ESMTP Postfix (Ubuntu)
>>>>    ehlo test
>>>>    250-backend.mydomain.com
>>>>    250-PIPELINING
>>>>    250-SIZE 104857600
>>>>    250-VRFY
>>>>    250-ETRN
>>>>    250-STARTTLS
>>>>    250-ENHANCEDSTATUSCODES
>>>>    250-8BITMIME
>>>>    250 DSN
>>>>
>>>>
>>>> HELO from Dovecot proxy:
>>>>
>>>>    220 proxy.mydomain.com Dovecot ready.
>>>>    ehlo test
>>>>    250-proxy.mydomain.com
>>>>    250-8BITMIME
>>>>    250-AUTH PLAIN LOGIN
>>>>    250-BURL imap
>>>>    250-CHUNKING
>>>>    250-ENHANCEDSTATUSCODES
>>>>    250-SIZE
>>>>    250-STARTTLS
>>>>    250 PIPELINING
>>>>
>>>>
>>>> When a client sends BDAT, Postfix closes the connection. Here's a 
>>>> log snippet from Postfix:
>>>>
>>>>    < MAIL FROM:<user at mydomain.com>
>>>>    > 250 2.1.0 Ok
>>>>    < RCPT TO:<some at recipient.com>
>>>>    > 250 2.1.5 Ok
>>>>    < BDAT 114098 LAST
>>>>    > 502 5.5.2 Error: command not recognized
>>>>    < Content-Type: multipart/alternative; 
>>>> boundary=Apple-Mail-55D35F74-2EB7-4B3B-A607-E421DD71C07A
>>>>    > 221 2.7.0 Error: I can break rules, too. Goodbye.
>>>>
>>>>
>>>> Apple Mail seems to ignore the fact that Postfix does not understand 
>>>> BDAT and Postfix does not like that :-)
>>>>
>>>>
>>>>  From a quick glance at the code it seems CHUNKING is always added 
>>>> to the capabilities and that's not configurable. Is this a bug or am 
>>>> I doing something wrong?
>>>>
>>>>
>>>> Thanks,
>>>>
>>>>   Michael
>>>
>>> that "may" version depend
>>>
>>> http://www.postfix.org/features.html
>>> ...
>>> Postfix 3.4     SMTP server support for RFC 3030 CHUNKING (without 
>>> BINARYMIME).
>>> ...
>>>
>>
>> As far as I understand, Dovecot always adds certain capabilities. This 
>> is the responsible code (I think):
>>
>> https://github.com/dovecot/core/blob/c8d03c3cab68328947a5afb47f48aef5b5a1e4ab/src/submission/submission-client.c#L95 
>>
> 
> Dovecot adds the capability to the server side (facing the client), but 
> not on the proxy client side (facing Postfix). If Postfix doesn't 
> support CHUNKING, Dovecot will translate between BDAT from client and 
> DATA towards Postfix. That's the way it is supposed to work anyway. I 
> cannot reproduce your problem here with a quick test.
> 
> Can you enable mail_debug=yes (e.g. for that particular user) and show 
> me the debug log of the proxy activity?
> 
> The output from `dovecot -n` would also be helpful.
> 
> Regards,
> 
> Stephan.
> 

I think I found the problem:

I am not using the submission_* config directives to configure the relay 
SMTP server.
Instead, I'm using Dovecot's proxy feature for selecting a backend 
server based on the user's authentication. The submission_* directives 
are all unset.

When using the submission_* directives, Dovecot translates from BDAT to 
DATA. With my configuration, it seems to just relay all the commands to 
the backend server.

Now that I think about it, I'm not sure what dovecot can do in this 
case. It doesn't really know the supported capabilities until the user 
authenticates themself.


Regards,
   Michael