Submission service capabilities listing

[Stephan Bosch]

On 13/11/2020 00:48, Dan wrote:
> Hello all,
>
> I'm attempting to implement a submission server with questions in 
> regards to how Dovecot handles the backend hosts capabilities. To my 
> understanding, Dovecot will connect to the host specified in either 
> submission_host or submission_relay_host, and gather a list of 
> capabilities. Once gathered, after the client sends the EHLO greeting 
> Dovecot will respond back with capabilities that the backend host is 
> capable of.

The submission_host setting is not relevant to this topic. It is only 
used for sending messages produced by Dovecot itself, e.g. from Sieve.

> My question is, When does this occur?

The automated part only works after AUTH. The initial EHLO is not 
necessarily accurate.

You can configure |submission_backend_capabilities to set the backend 
(=relay in this case) capabilities directly. In that case the backend 
EHLO reply is not used.|

> Running a tcpdump with the filter set to the relay host IP, I don't 
> see any traffic until after I send the EHLO command. Dovecot states 
> that CHUNKING is available, but the backend host does not have that 
> capability.

CHUNKING does not need backend support. The mail can be accepted using 
BDAT command at the frontend and relayed to the backend using classic 
DATA command.

> Is there a way to disable CHUNKING explicitly?

You cannot currently disable CHUNKING support at the frontend. Why would 
you want to?

Regards,

Stephan.

>
> Thanks.
>
>
> submission_relay_host = x.x.x.x
> submission_host       = x.x.x.x
> submission_relay_ssl  = no
> submission_relay_ssl_verify = no
>
> protocol submission {
>   passdb {
>     driver = static
>     args   = host=x.x.x.x proxy=y nopassword=y port=587
>   }
> }
>