I considered that option. But the time lapse seems to be too big with such an approach. Is there any way to check if the owner has another email address that he actually uses?
Other than Whois, I'm really not sure. I guess you could try a contact form if their website has one, and if worst comes to worst, try and hire a broker or something using Sedo or whatever service you prefer.
if you simply don't get answer, then its their right but you can try simple to send them letter.
If you get not successful delivery notification, because email don't exist, maybe contact their registrar, i think it must be working email.
I wouldn't recommend that for several reasons. The person selling the domain may see the post and spike prices way up or something and overall it just isn't a good idea.
you could try calling at his phone number if that info is available from whois, but i don't think the owner of that domain would like to get a phone call from some stranger unless you offer a good price for his domain.
its not one name but a whole bunch of names, the kind that usually aren't up for sale (LL, LN.nets).
I think this is an important question because there would be a time in every domainer's life when he would want a name bad and there would be no way of contacting the seller.