Today, I sent an E-mail to a peer, with a document attached explaining what an E-mail is, including a diagram with description to how an E-mail works, as shown below.

About E-mails

E-mail is an abbreviated form the term ‘Electronic Mail.’ E-mail is a store-and-forward method of writing, sending, receiving and saving messages over electronic communication systems. The term ‘e-mail’ applies to the internet e-mail system based on the Simple Mail Transfer Protocol, to network systems based on other protocols and to various mainframe, minicomputer or internet by a particular systems vendor, or on the same protocols used in public networks. E-mail is often used to deliver bulk unsolicited messages or ‘spam’ but filter systems exist which can automatically block or delete some or most of these.

(Diagram here)

The diagram above shows a typical sequence of events that takes place when someone composes a message using their mail user agent. They type in or select from an address book, the e-mail address of their correspondent and then press’ the send button. Their MUA formats the message in Internet e-mail format and uses the Simple Mail Transfer Protocol (SMTP) to send the message to the local mail transfer agent (MTA).The MTA looks at the destination address provided in the SMTP protocol (not from the message header).An Internet e-mail address is a string of the form localpart@exampledomain.com, which is known as a Fully Qualified Domain Address (FQDA). The part before the @ sign is the local part of the address, often the username of the recipient, and the part after the @ sign is a domain name. The MTA looks up this domain name in the Domain Name System to find the mail exchange servers accepting messages for that domain. The DNS server for the b.org domain, ns.b.org, responds with an MX record listing the mail exchange servers for that domain, in this case mx.b.org, a server run by the correspondents ISP.
smtp.a.org sends the message to mx.b.org using SMTP, which delivers it to the mailbox of the user. The user presses the "get mail" button in his MUA, which picks up the message using the Post Office Protocol (POP3).