You have to understand a few things about the Internet and how information is exchanged to understand how email works.
If you are online for any reason, you probably have an email account that you use for either business or personal communications.
Most of the time, email is instantaneous, or at least it would seem so.
Email can often take a very long route to get to you, though it depends on where it is going and from where it is coming.
Your computer is a terminal that connects to other computers.
The Internet is nothing more than computers networked to each other.
Each webpage that you visit is stored on a server - or a computer - somewhere.
When you type in the name of a website, your computer uploads information from another computer somewhere so that you can view what is on that page.
This is done very quickly with a series of commands that are probably unknown to you.
Your email works in the same way.
If you use Yahoo, for example, all of the information you see when you open your email is contained on their servers and computers.
This means your computer asks Yahoo for information and you see what is in your inbox.
If you send an email, you go back through their servers to send out that information.
An email will go out as an information packet.
This goes first to Yahoo, and then Yahoo sends it on through routers placed throughout the country.
Which routers they use will depend on where your email is going.
Your packet travels until it gets to the server of the email provider your recipient is using.
They can then request their email through their computer in the same way that you do.
This often takes only seconds to complete.
Now that you know how emails get to you, you can understand how it might be possible to trace an email that comes to you from an unknown person.
Look for a free email search that can tell you a name to go with that email address in some cases.