Before working with e-mail, we need to understand a bit about how e-mail works, as well as what it provides and what our application needs to perform on its own. In general, e-mails are easy to understand—someone sends a message, the e-mailing system takes care of delivering it to the correct target machine(s), and the recipients are then able to retrieve that message. From the e-mail system's perspective, it does not care about what the e-mail contains, as long as it knows who it is from and who it should be delivered to.
From the user's perspective, he/she does not need to know how it is delivered—their mail application delivers the message to the server handling their e-mail, and all messages can be retrieved from that same server. When we interact with e-mails, it works the same way for us. In the majority of cases, our application only needs to interact with our e-mail server.
All e-mail messages are built using a common structure—each message consists of headers that...
