Mail domain, letters to gmail do not reach?

Question

PHP

at first, mail, except for Yandex, did not go anywhere from the script through mail () turned on DKIM and DMARC on the server, letters began to reach mail.ru. but gmail does not even get into the spam folder. not coming.
those vds support answered that everything is ok on the server, they come to gmail through the console. through the mail program on the Roundcube server, letters leave but end up in spam. I need to send a notification through a script.
As I understand it, you need to set up the mail domain correctly, so how to set it up so that everyone receives letters?

Answer 1

The issue was resolved
the problem was that the standard sending
not all headers go away and the letter is not signed. so gmail blocks unsigned ones.
Solution: send letters through the smtp class, all headers go away, letters reach.

Answer 2

Is everything else in the letters correct? In service headers (Subject, From, To, etc.) only 7-bit characters, if there is an HTML part, that is, the corresponding PLAINTEXT part, are SPF and DKIM configured correctly?