Can't send mail to domain @optima.com.ua

Hi i try to send email from my <any mail>@<my domain> to every email on domain optima.com.ua end get returned error

Undelivered Mail Returned to Sender

For example from admin@v-e.com.ua or any my email to trei@optima.com.ua . My friends who have domain email cant send to optima.com.ua too.

trei@optima.com.ua , ERROR_CODE :573, ERROR_CODE : admin@v-e.com.ua unknown user account

Received:from mail.zoho.eu by mx.zoho.eu