Not all letters from the site come from Yandex traffic rules. Why?

Question

Email

Question from the teapot.
There is a site on reg.ru, mail is delegated to Yandex. Most of the letters come to the Yandex mailbox, for some part they settle in the mail client reg ru (roundcube). Emails are not marked as spam. Can you tell me why this is happening and how to fix it?

Answer 1

Hosting support replied that for Yandex mail to work correctly, it is necessary to delete the mail domain on the hosting.