I am getting multiple copies of one email and fail to understand why? (Repeated Emails)

The most common reason for receiving repeated emails can be explained using an example. You’ve created an email-id a@yourdomain.com and forwarded it to itself and b@yourdomain.com. Now you have both the email-ids configured in your email client and if someone sends you an email at a@yourdomain.com, you are bound to get 2 copies for the same message (one for a and other for b account). This is the basic concept which can become a more complex one if you have number of email-ids on your domain and you do lot of email forwarding between those email-ids.