Dovecot submission announces CHUNKING but backend Postfix does not support it

[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