For contacting potential end users i would suggest depending on the type of niche the domain relates to browse i.e. the net/yellow pages for finding prospect buyers.
Say for instance you have the domain, NewYorkRealEstate.com, i would find and contact as many businesses/individuals involved with Real estate by looking up their contact info on their current website or sending a letter/fax.
You would only want to contact relevant businesses & individuals (realtors) to market your domain to and not every email address you can find or get your hands on.
If English is your native language and your a fluent speaker and you're comfortable with -
cold calling - then calling prospect buyers is in some cases more effective.
But i would not reconmend it if you're inexperienced. But if English is your native language and you speak it effortlessly it's one barrier less you would be confronted with. The next step would be to do your research on cold calling techniques, common associated pitfalls, etc.
Then you would need to overcome the most common barrier people endure doing their cold calling, they feel uncomfortable trying to sell something...
Good luck!
