It can be very scary to receive harassing or threatening email in your inbox. Anyone who has been targeted by this type of email knows that it can be extremely upsetting- especially since you generally don't know the identity of the person behind it. Is this a real threat? Is this some kid who thinks it's a funny prank? Does this person know me, who I am, where I live? These types of questions can keep a person awake at night. If you receive an email like this, the most important thing to do immediately is to save the email- don't delete it. Not only can it serve as powerful evidence later, but it can provide the very information the authorities will need to track down the perpetrator. This important information is hidden in the email header.
Most emails do not show a full header. The header you normally see is a compact version that shows only the 'to' and 'from' email addresses and the time at which the email was sent. In normal circumstances, this is all the information you need. But when it's a matter of harassment or threats, the full email headers can provide authorities with enough information to find the exact location and identity of the person who sent the email. In fact, there is very little the authorities can do without the information contained in the headers.
In your email account, there is usually an option that will allow you to display a message's full header. It is usually an option you can click while you have the offensive email open. But if you have trouble finding it, a simple email to the email provider's customer service department can answer any questions you may have about finding the header. Once you know how to display the header, you can forward an email to the perpetrator's email provider (a customer service department or a dedicated abuse department) with the full email headers intact. Email providers take these complaints very seriously and will respond accordingly.
One very important piece of information contained in the email headers is the IP address. To avoid any confusion, it is important to know that this is not the IP address of the perpetrator in most cases. Ninety percent of the time, it is the IP address of the person's internet service provider's server. Make no mistake, the ISP can use the information in the headers to find out exactly who is bothering you, but they will not give the person's name or any other information to you, a private citizen. In most cases, they won't even provide it to the authorities without a court order. While there are tools available on the internet that will help you analyze the headers in any email you receive, the information will probably not prove useful to you in putting a stop to email harassment without help from the authorities. The best course of action is to save the email and enlist the help of local law enforcement and any other establishment that may be able to help, such as your own and the perpetrator's email providers.