access externally to OWA and ECP from public IP

Assuming my domain name is xyz-company.com and I have a public http://www.petenetlive.com/KB/Article/TechTerms#IP address of 234.234.234.234

why i can access externally to OWA and ECP from this public IP 234.234.234.234/ecp  i need to block this public IP without effect that i can access with mail.domain.com/ecp from externally