i ham having challenges when sending emails and the receipients in my email list is more than 9,10 or more the email is not able to deliver i need help

these are my email addresses yacub@koro-integralmarine.com info@koro-integralmarine.com operations@koro-integralmarine.com opr_tema@koro-integralmarine.com i a able to recieve emails with several reciepients copied in the email list, but how ever and not able to reply or send email to a reciepinet list more than 8 as areply or as an independed email that am sending where i wish to copy more than 9 or more reciepients kindly up