I have a small company in Greece. Its website is www.slas.gr 

My email is *** Email address is removed for privacy ***.

Recently I discovered that slas.gr recieves emails from any other mail except of @hotmail.com.

So when I send an email for example from  *** Email address is removed for privacy *** to *** Email address is removed for privacy *** I get a Delivery Status Notification ( Delay ) and then a Delivery Status Notification ( Failure )  

Could you pls help as it is important for my company?