Email Domain?

[JUNG2]

For some reason someone has been able to use our Email domain name without our authorization. Example, Lets say our domain is called (mydomain.com) and all our email would look like name@mydomain.com. Today I recieved an email with an email address that is not on our list but with the same domain (ex. unauthorize@mydomain.com). How can I prevent this

Thanks

[Statica]

You literally cannot prevent it from happening, other than sending an email to the admin of the mail server or the sender's IP; asking them to take common measures like turning off relaying etc.