Why do all emails from sites on VPS with ISPmanager go to spam or don't reach?

Question

Email

Please tell me how to set up sending notifications from forms on WordPress sites using the mail() / wpmail() php functions so that they come to incoming messages, and not to spam?
What is the best and/or easiest way to set up this submission for multiple sites on a server? In the future, their number will increase. This is me to the fact that for one particular site it was not necessary to do so many manipulations. For each domain, creating a mail domain, a mailbox, adding several records is a rather cumbersome solution :) I
used shared hosting earlier and had no such problems. Please help with detailed settings for sending emails from the server to ISPmanager :)
UPD: in the php mail() function in the FROM header I write [email protected], and Yandex.Mail receives a spam letter with the actual sender address - example.com (nothing comes to gmail at all), maybe this is the main problem ? Where does this address come from in the almost "naked" ISPmanager, maybe someone came across, please tell me :)
Server: cloud KVM from REG.RU
Panel: ISPmanager Lite 5.182.3

Answer 1

Thank you all for the answers, they are useful, but the answer from REG.RU technical support became decisive, because with the "left" sender, nothing but spam came.
The sender's address is specified in the php.ini file of the version of php that the site uses. Usually such files are located in a directory like /var/www/user/data/php_version/php.ini. At the very bottom there is a [ISPmanager] settings block. You need to find the sendmail_path in it and replace [email protected] with mail based on your domain, which is unfortunate.
To send to the main mail services, it will be enough to configure the SPF record, the hostname on the server and the PTR record for the IP. With gmail it will be more difficult. Here you can already set up a DKIM signature and send via smtp with authorization, but the harsh google filter can still mark such emails as spam. In this case, you can try to train the filter. To do this, mark messages as "Not Spam".

Answer 2

Because you need straight arms :D

Answer 3

ispmanager is hardly in business.
send mail via smtp.
install the appropriate plugin on vp and configure.
Link the domain mail to Yandex for reliability.

Answer 4

Bad ip, bad neighbors. Send via third party API or PHPMailer or something like that

Answer 5

As mentioned above, you need to add an SPF record to your domain, this will increase the chance that letters will not fall into spam. If you add a DKIM signature, it will be generally gorgeous.

Answer 6

https://www.mail-tester.com/
Send a letter here, see the reason for getting into spam. If it is not clear what the points mean, google and correct.
At a minimum, you need to configure PTR and the correct hostname on the server. It's better to use local exim for these things and create mailboxes in ISPManager and then send via SMTP. DKIM do not forget to include more.