Why does Yandex mail not allow sending letters on the same domain?

Question

Mail server

The mail was created on the deltapolymer.ru domain via Yandex360. Letters go to everyone, but after sending to any. We tried with [email protected] and [email protected] on [email protected] immediately blocks mail and does not allow anyone to write.
"The email cannot be sent because it looks like spam. You may have sent too many emails today."

Answer 1

Answer from support
Hello!
This situation occurred due to the fact that the login registration of the administrator of your deltapolymer.ru domain seemed suspicious to our security system.
Now we have taken some measures. Please check, mail should work fine.
We recommend that you specify reliable personal data in Yandex ID for the domain administrator account. Attach your mobile phone there, if you haven't already. You may be prompted for captcha (control characters), enter it

Answer 2

Good afternoon!
You probably have a lot of spam complaints about your emails. This is indirectly confirmed by the presence of your IP in two
blacklists https://mxtoolbox.com/SuperTool.aspx?action=blackl...
Also, the reason may be a hacking of your site or one of the mails.
Yes, and bind the phone to the mail-administrator. Also try to take a break of 24 hours in sending, this sometimes helps.