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 } }