This is actually a very glaring flaw in the IP networks, but the flaw is a necessary evil. It is convenient to make emails like these very easily because the Simple Mail Transfer Protocol which is actually the IP protocol that determines mail passage in the TCP/IP connection of networks has no guard against these spoofing. All that is required of the sender is a name in which the mail will be sent. This is probably done to promote more business opportunities but almost all the time it becomes a humongous hassle.