Why does Mail.ru block letters from the site if the sender points to @Mail.ru?

Question

PHPMailer

Good afternoon!
I encountered such a problem: the site has a feedback form, letters from this form come to the mailbox on Mail.ru in the FROM line there is the sender's e-mail address, which he indicates in the form on the site. The problem is that if the sender specifies mail from the @mail.ru domain, then the letters do not reach, they do not even end up in spam, if you specify any other domain, for example @gmail.com, the letters arrive without problems.
Tell me what could be the problem? However, until recently everything was working fine.

Answer 1

I think this is the reason - https://habrahabr.ru/company/mailru/blog/282602/
A letter sent from your hosting directly does not pass this check.

What should I do if...
...I'm using a public mail return address to send emails via scripts on the server
This shouldn't be done...