When an email is sent, several elements give an indication about the message source, including the visible address of the sender, and the technical shipping address. These two addresses must exist, but it is also possible to provide an additional address for the specific purpose of receiving the answers.
The purpose of this article is to clarify the usability and operation of each of these elements.
The visible address of the sender and the return address are determining elements for the sendings reputation. These elements are represented by headers, which you can find in the source of the emails that you receive.
The diagram below shows the analogies between paper mail and e-mail items: