Due to the way that email works (specifically
the SMTP protocol) it is possible for anyone to put anything they like
in the "From:" field of emails that they send. This makes the email
appear to be from someone else.
This is a fairly common practice among spammers in order to conceal
their identity. There is, unfortunately, really very little that can be
done about this. The email could be sent from literally any person using
any mail server in the world. Tracking them down is extremely difficult
and time consuming (if it is possible at all) and even if you do manage
to track them down they are typically in foreign countries making any
kind of legal remedy virtually impossible.
The problem is exasperated by the fact that there are many viruses that
will take over an infected machine and randomly generate email using
names and addresses found on the infected computer. All it takes is for
someone, somewhere, who is infected by such a virus to have your email
address in a document, address book, or email stored on their computer.
These virus generated "waves" of spam and fake emails tend to slow down
over time and eventually fizzle out as those with infected computers
either remove the virus or the virus does something to destroy all data
on the machine that hosts it.