When to the DKIM SPF DMARC mail setup location?

Question

SMTP

Good afternoon,
I ask for help. I just started to figure out how to send mail.
At first I tried to send via mail (), but everywhere they write that it is better to use smtp.
The site has already implemented the smtp class with fsockopen().
There is no special mail domain for the site on the hosting,
it is assumed that mail will be sent from smtp.yandex.ru. And in response to filling out the form on the site,
it was sent without problems to both Google and Yandex.
When it was necessary to do a cron mailout 3 times a day and use an array of addresses,
then everything began to work very strangely: sometimes it doesn’t come anywhere at all, sometimes it only comes to our domain,
sometimes comes to gmail.ru, but always ends up in spam. Since sometimes it comes, then, apparently, the code is working,
but the point is something else.
In the incoming letters it says "Our site '' through othersitename.org, that is, as if not from our site. I broke my head what to do for the correct sending: set up a mail domain on the hosting (you can register DKIM SPF DMARC there)? In Yandex, register such settings (I don't know if this is possible, I do
n't have access yet)?

Answer 1

1. mail() uses smtp - so that's complete nonsense, how the server sends this is already his task, but from the point of view of php, the mail is completely valid.
2. There are a million implementations, so you can use a regular mail and specify in the php.ini settings that msmtpd, for example, will be involved in sending, and postfix itself can work perfectly with an external mail server in repeater mode.
3. Yandex connect - this is mail for your domain on Yandex.
4. On Yandex Connect, you can fully maintain the DNS zone with the editor and for free, it is possible to generate both DKIM DMARC and SPF, of course, too.
to do this, you either delegate the domain itself to Yandex and request the keys there
or simply copy them in the connection.
Well, or use the API to request DKIM keys (there we will wash the usual CURL)
as well, the departed mail leaves logs, don't forget about it

Answer 2

Always in place if you want mail delivered. And the human hostname and PTR are also important.
https://www.mail-tester.com/

Answer 3

That is, did it bother anyone at all that a "left" domain is added to the topikstarter's domain, given the fact that mail goes through the Yandex server?