dovecot - Jan 2023 - submission_host auth

When using dovecot container with sieve plugin there is no sendmail to use for
sending email for sieve redirect action for example. We can use submission_host
instead https://doc.dovecot.org/settings/core/#core_setting-submission_host but
there is no way to specify credentials for auth in remote MTA.
Submission_relay_* settings e.g. submission_relay_master_user relate to dovecot
submission service. Using something like permit_mynetworks in remote MTA is not
acceptable for security reasons.

Is it possible to add authorization in the remote MTA using submission_host?

> When using dovecot container with sieve plugin there is no sendmail to use
for sending email for sieve redirect action for example. We can use
submission_host instead
https://doc.dovecot.org/settings/core/#core_setting-submission_host but there is
no way to specify credentials for auth in remote MTA. Submission_relay_*
settings e.g. submission_relay_master_user relate to dovecot submission service.
Using something like permit_mynetworks in remote MTA is not acceptable for
security reasons.
> 
> Is it possible to add authorization in the remote MTA using
submission_host?

You start the auth service in dovecot, then tell the MTA to use it.
For example, if you use postfix this explains how:

   https://doc.dovecot.org/configuration_manual/howto/postfix_and_dovecot_sasl/