JohnFK said:
So unless you are LE with a search warrant or special powers, nobody can actually trace an IP address to John Doe of ABC Street, Anywhere, ON for example?
Basically, yes.
IP addresses are almost always dynamic for home users, meaning they are assigned by the ISP at random and will expire at specified intervals. When it expires, the customers' modem requests a new IP and it
may be assigned a different one. You'd need the proper public IP address assigned to their modem and a timestamp of the offense -- LE would then need to be involved because ISPs have to abide by privacy laws and won't just hand out their log files to civilians. If you had the proper evidence you could try reporting it to the ISP yourself, but they would likely deal with it internally.
Then it gets even more complicated because if someone did know the 'where' and the 'when', they could wind up having a wireless router with an open access point.
If this is related to public web mail like Hotmail or Gmail, you will probably never be able to get the proper IP address to point you back to their ISP -- you'll just see IPs from one of Google's or Microsoft's hundreds of mail servers...
It's not impossible, but it would require a lot of work and the offense would need to be worth it, so to speak.
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Here's a handy utility you can use to extract the useful information from an email header:
Parsing and Tracing Mail Headers