• After you compose an email and press send, it is sent as stream of packets using the Internet's TCP/IP protocol. Each packet bears the address of the destination, among many other kinds of information, such as the address of the sender.
• Routers on the Internet look at the addresses in each packets and send the packets on the best path to get there. Many factors go into how the packets are routed, including the traffic volume on various backbones. Each packet might take a different route, so the email packets can arrive at the destination out of order.

How an email list works:

• Email mailing lists are a way for groups of people to have public discussions via email. After you join a mailing list, every message you write to the list can be read by everyone on that list.
• To join a mailing list, you must subscribe to it. You subscribe by sending an email message to the mail list administrator and asking to join the list. To cancel your subscription to the list, you must send a cancellation request to the list administrator.
• The email mailing list itself is a database of email addresses of people who have subscribed to it. When you asked to subscribe, you are added to the database.
• When the computer on which the database resides receives a message to be sent to the mailing list, it automatically sends the message to every address in the mailing list database. Some mailing lists are very active, and people on them can receive dozens of messages daily. Because of that, it's a good idea to check your mail frequently and clean out your mailbox. Otherwise, it’s possible to bog down your mail server, which can make it difficult for you to read your mail because you'll have so much of it.