How Email Works
Now that we have all the components and understanding of those that we need, how does it all actually work together to operate a system of emails?
Without going into a chicken and egg situation – let's begin with the creation of the email from a desktop computer through to its reading by on the recipient's desktop computer…
Computer/PDA/Mobile Phone/Other ---> SMTP mail server ---> DNS server ---> Incoming POP3/IMAP server ---> recipient's Computer/PDA/Mobile Phone/Other
As everything else on the internet, these email messages may pass through several different servers to actually end up where it is intended to go (the internet does not have a central hub as such, it is composed of many, many computers of various descriptions connected together as a net, not as one single system). We wont mention those various ‘hops' here, they could be anything at any different time of the day, week or year.
Now let's consider what happens when someone sends you an email in the same fashion…
You'll notice that we are now using server descriptions like SMTP, POP3. We'd better take a quick look at what these are. A mail server is simple a computer system with a means of storage that is constantly connected to the internet. That means of storage is normally a hard drive – you may now be thinking that it resembles something like your desktop computer, well it does in some respects, but you wont see someone sat at it with a monitor playing Spades. It is a dedicated machine, and which has administrative access usually through a separate desktop computer.
This mail server has two key components which involve emails.
There is the SMTP ‘outgoing' server component which is used to receive email from an account and which is addressed to someone else's account. In other words, each time you send an email, it goes to your SMTP ‘Outgoing' server for handling, this handling is undertaken in a matter of seconds or split seconds during which it determines where the email is destined.
The other key component is the POP3 or IMAP (incoming) server, which is used to receive email that is addressed to you. You can access your emails on this server using your email client or via a web page interface as discussed previously.
The two components go on to make up the mail server, and you will notice that many email service providers require the separate mail server settings in your email program set as the same – i.e. some mail servers are mail.domainname.com (domainname is replaced by the actual name of their domain (such as AOL, Yahoo, etc, etc) for both SMTP and POP3/IMAP. Whereas other servers may show two different server names, such as pop.domainname.com and smtp.domainname.com. Either way, the incoming and outgoing emails normally end up on the same machine. It is just that they are stored according to their route – in or out.
The DNS server is another computer system which determines where the email should be sent next – in other words, it takes the address and determines where the recipient stores their incoming messages, and finds the most appropriate route to send that mail on its way to them. The DNS server could be considered to be like a partial map with indications of where to go next to get to a specific point. As we said earlier, an email can take many ‘hops' at various servers around the internet to actually reach the incoming mail server of the recipients.
All of these services rely on some simple text code that every email has buried at the very beginning of the message. This is called the Message Header and it can contain various pieces of information and always at least the sender's email address, the recipient's email address and the date and time that it was sent. This bits of information are used by the servers to determine what they should do with the email message and they also allow the POP3/IMAP mail server to store your received messages all in one place that you can later retrieve.
What does POP3 mean?
POP3 stands for Post Office Protocol version 3. This has nothing to do with the Post Office that we know of in the local High Street or shopping centre. This is what the protocol was called upon invention. Its intended use is for message handling via a third party software program such as Microsoft's Outlook Express or Netscape's Composer to name but a few. From your stand point POP3 stores and handles all your incoming mail.
What does IMAP mean?
IMAP stands for Internet Mail Access Protocol and is pretty much the same as POP3 except that when you use your mail software to access by this method, the mail messages remain stored on the ail server unless you decide to actually delete them. This is more flexible than IMAP since it gives your access method more freedom – you will be able to access the same messages many times over and from wherever you decide to. Also, it offers you more security in terms of loss of data. If your desktop crashed to the extent that you lost your email data and messages, POP3 would not be able to offer you a means to retrieve them as would IMAP, which retains copies on the server. The other difference to consider is that IMAP can take a little longer to access and send or receive emails than POP3, but this is may be negligible on some systems. The IMAP mail server handles email that is leaving you and is destined for other people. From your stand point IMAP stores and handles all your incoming mail.
What does SMTP mean?
SMTP stands for Simple Mail Transfer Protocol and is takes the form of server which handles all your outgoing mail and it communicates with many other SMTP servers to send it on to the intended recipient(s).