How to organize the sending of letters?

Question

PHP

It is necessary to send letters to users if:
1) The user has registered (confirmation)
2) Password recovery
3) Application in the panel
4) New order
5) Single sending from the system to the user (rarely)
As you can see, no mailing, no spam, only single sendings to users in case with point 3 (application in the panel), frequent shipments are also possible.
So, what is the best send mechanism to use? I thought that it would be easier to create mail for the Yandex domain, register an [email protected] mailbox and send letters via smtp (php) to users via ([email protected]) on their actions.
Is the diagram correct?
Do I need additional manipulations with DKIM in this case? (I tried to send via smtp regular mail on Yandex, the digital signature status was correct, so there are no problems with DKIM?)
Are there any restrictions?
p/s I looked here https://yandex.ru/support/mail/troubleshooting/sup... but there is not an understandable table, I did not understand how much I can send in this way.

Answer 1

If you don’t want to raise your own mail server and prescribe everything to it as it should, including SPF, DMARC policies and the DKIM signature, then everything is reasonable.

Answer 2

You can send from the server itself.
But in principle the scheme is correct.