The have found most important thing is to contact the right person, the decision maker in the company
Dont just contact the WHOIS address of a company and think you will always get a reply, there are ways (Google, LinkedIn, Bloomberg, Yahoo Finance etc) you can find out who the top execs are and contact the right person (Business Development Manager for instance)
I have emailed a company (whois address) and got no reply and emailed the right person 3 weeks later and made a sale so it makes a big difference
I have emailed from my hotmail and also from an email address associated with the domain I'm selling and made sales using both methods
Hope that helps...