There is a form. Letters go to my mailbox at example@gmail.com If the senders indicate mail to mail.ru/yandex.ru then the mail does not arrive, and if you specify something else, for example, user@over.rucom, then the mail comes. And if I send to the mail and indicate the gmail box, then a letter arrives, but with a note that they cannot verify the authenticity of the sender.
Can you do something about this? and why is this happening