Flexible SMTP setup?

Question

SMTP

I set up Yandex mail for a domain with my useless domain and all letters began to arrive normally to the recipients in the inbox. But having multiple accounts is a pain in the ass, so you need to set up hmailserver to work with scenarios:
Scenario 1:
Mail is sent from local to local via local SMTP.
Scenario 2:
Mail from external servers arrives at the local server and reaches the destinations.
Scenario 3:
Mail is sent from a local address to an external address, arrives at a local SMTP server, and in its general (original) form is redirected to an SMTP gateway from Yandex (mail for domain) and delivered to recipients from there.
Please, tell me how to set up a mail server in this way?!

Answer 1

Scenario 1 already works for you regardless of external traffic rules, inside you at least send it from [email protected]
Scenario 2 will not work because Yandex does not have a forwarding functionality at the level of traffic rules, but you can individually arrange the rules for forwarding to a private domain, let's say you did @mydomain.ru on the traffic rules, do @private.mydomain.ru for yourself and in the box you do the forwarding - Yandex will resolve the MX and deliver it to you mail to your mailserver.
Scenario 3 - via Yandex SMTP + authentication and substitution of the sender's domain (using scripts on the hmylserver - it allows you to manipulate headers in VB) - I believe you can achieve what you want.