To "calculate" the mysterious Mr. X, you'll have some time to turn into Sherlock Holmes. Because the desired subject is not left a clear information. Immediately it is worth noting that there are no guarantees of success there, a lot will depend on coincidence.
Arm yourself with the search engines. If the mailbox owner you want to know used living real person and not a bot, he could leave information about yourself in the Internet-pagers, forums, chats, social networks or in the blogosphere or it there could discuss. In some cases, you will find a real person's name and other data.
Please note: if on many sites this information is private, then the cache of some search engines it may happen to be in the public domain. The events of the summer of 2011, when more than 5000 SMS private character was in the public domain - a clear indication of the importance of using search engines in establishing the identity of the owner of the email.
Try to strike up a correspondence you are interested in the person, using a false account in a mail service. Often, people give information about themselves, if familiar some time (even virtual).
If its own forces are insufficient, but are you willing to splurge a bit, refer to the detective Agency. After all, professional investigators have a wider range of opportunities to find people, and in the Arsenal they can be helpful equipment. Tell the detectives all the information put before them a clear task. Is to immediately question the cost of services.
Turning to the detective Bureau should not overlook the following points: how long does the company exist, whether there is positive feedback about these detectives, what portfolio they can offer you. Beware of scams and shell companies, pretending to be a decent detective Agency.