Receiving an email from a anonymous sender can be annoying, troubling and even frightening. Email allows the sender to hide behind any number of smokescreens (fake email accounts, anonymous e-mail services, etc.), but there are a few things you can do to make an educated guess about who sent the mysterious message.
Mining the E-mail for Clues
Read the message carefully. Did the sender write something only a few people would know? If so, think of who is most likely to know that information. This will help you narrow the possibilities.
Examine the address. Sometimes, novice emailers forget that their name shows up even if they don't sign it in the body of the email. Even if it doesn't, look at the domain name. It might tell you where the person works (if the email was sent from a work account, or works for a website.)
Get the IP address. An IP address is like a computer's fingerprint; each one is unique, and you can quickly pinpoint that computer's location. In Microsoft Outlook, for example, go to View -> Options, and look at the Internet headers. The information will tell you the IP address of the machine that sent the email. Many web sites offer free IP address tracing.
Consult the authorities. If the message was threatening or suggested plans or knowledge of a crime, police may investigate. Chances are, if the person used an anonymous email service, the message could get them in trouble. The email service may not be obligated to tell you who sent the message, but the police stand a good chance of getting that information if the service knows a crime may have been committed or may be committed.