Can't create email info@eko.edu.vn

Can't create email info@eko.edu.vn

Hi Zoho Team,
My domain if eko.edu.vn. I want to create user named info@eko.edu.vn. But everytime i click Add users and input parameter "info", press OK. Then I received this message telling that the email is exist. I check the invitation list then I see there is an invitation for this account.
can anyone help me?
thanks a lot,