It can be a frustrating situation.
I am saddened at how often I get questions similar to this.
Sadly, the answer for most people is simple: you don't.
So what can you do?
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Who sent email?
You can't trace the origin of harassing emails to an individual or address without law enforcement's help. Email headers offer limited clues, but most platforms don't have the level of detail you'd need. Even with an IP address, tracing the sender requires legal help.
You cannot trace the source
Each time I write on this topic, I'm flooded with even more requests similar to this one, which shows that folks have missed the point of the article. I don't mean to be rude or obnoxious, but I need to be excruciatingly clear at the outset.
If the sender of an email does not want to be identified, and if the email does not identify (perhaps accidentally) who it's from, there's no way for you as the recipient of that email to trace it back to the person who sent it. Period.
Occasional clues
There are sometimes clues in email headers that you typically don't see.
In my article How Can I Trace Where Email Came From?, I summarize what those headers look like and what you might glean from them.
Unfortunately, applications like Facebook and other types of messaging systems aren't email at all. As a result, they don't have these headers. As far as I can tell, there's nothing available to message recipients of those systems to use in a way similar to email headers.
Using email headers, you can sometimes determine the "name" of the computer sending the email and its internet IP address. Often, the email is sent using web services like Hotmail or Gmail, in which case the IP address will be of Hotmail's or Gmail's own servers, not the sender's. Sometimes the services will include the internet IP address of the machine that actually visited the website to send the mail.
But even if you get the IP address, that's still not enough information to help you.
The IP address doesn't help
In another article, Can I Get Someone's Name and Address from Their IP Address?, I've explained that the answer is clearly "you can't" -- at least not without the help of law enforcement. An IP address tells you very little about the real-world location of the machine (or machines!) it represents. At best, you can usually locate the ISP responsible for allocating that IP address to actual users.
But once you get that far, you'll need help.
And that's where law enforcement comes in. Their response will vary depending on the seriousness of the charge, how seriously they take these types of issues, their expertise, and their workload.
Based on my experience with the sheer number of requests I get on this topic, I can only imagine that an already overworked justice system will be hard-pressed to give you any satisfaction. Your best bet may be to use methods unrelated to email, such as your son's school's social structure and dynamics -- perhaps with the aid of the staff there -- to determine who might be responsible.
Anonymous email is important
In situations like this, it's tempting to have a knee-jerk reaction that anonymity -- and in particular, anonymous email -- is evil.
Political dissidents, corporate whistle-blowers, and other individuals with important and sensitive information to share would disagree.
As would I.
Email is simply a tool that can be used for both good and evil.
Do this
At the risk of offending with redundancy, I have to reiterate the difficult truth.
Involve the authorities or law enforcement if the threat is serious enough; but even then, realistically you may not get the answer you're looking for.
Here’s something you will find useful: Subscribe to Confident Computing! Less frustration and more confidence, solutions, answers, and tips in your inbox every week.
i am being threatened by a man on a website and he is sent me this comment If I send him a letter thru the post office, You can not open it and throw it away! That is a felony.
Now get this When I send a letter to him or call him is up to me! I can do it today or next month if I want to. The fact that you will not know when I decide to do it, is the best part. I saw your threat on you other crappy story that because I haven’t come and left a letter or called so you are still here.
Get this I won’t just state That you are here but I have been coping all of your stories and replies. I will make sure I will give them to him and there is nothing you can do about that boy!
As I said I will send him a letter thru the post office and there is nothing you can do. I will send it certified so he is the only one who can sign for it! It will contain everything you said including what you said about your sister!
Get off this site and I will leave you alone get that!
now tell me does that sound like a threat he said he is my neighbor i have not seen him he said he lives on the next street how can i get him to stop
I open letters all the time and throw them away. I also throw away letters I’ve never opened. As far as I know it’s no felony.
This sounds like some kind of a creepy scam, but if you’re concerned I’d contact the local authorities for guidance.
I get at least 3 spam email every day but I just send to a file (I setup for Bogus). This way if asked by a investigator; I will have viewable emails to show them. It is just one way to keep track of them. I NEVER OPEN BOGUS EMAIL’S!
I just send those to the spam folder and regularly clear out the spam folder. Hanging on to them is useless. I don’t expect any government investigators to ask for them. I would keep any harassing emails, but I wouldn’t hold out much hope that it would do any good.