The #1 most important thing is to contact the right person at the company, the decision maker....
Check the company exec team on their website, LinkedIn, Google, Bloomberg, Yahoo finance etc and find someone who can make the call on whether to buy the name (ie the business development manager, CEO etc). For example, If you Google "Cisco Executive team" for instance, it comes up with this -
https://newsroom.cisco.com/exec-bios, so its not hard to find the right person. If you Google "Cisco Email format", it comes up with this -
https://rocketreach.co/cisco-email-format_1063
So its not hard figure out the person's email either. I find LinkedIn a very useful resource for this and to find out the founder or CEO's name.
For smaller companies that may not be in Bloomberg or Yahoo Finance etc, sometimes you can google something like "company name CEO" or look on LinkedIn and then find the persons name and then work out the email from there. You can search a company on LinkedIn and then click "People" down the left hand side and it will show you a list of people who work there with their job titles.
If you email the WHOIS email or something like
[email protected], it will more than likely get deleted or not reach the right person.
This is just what works for me and can be tweaked to suit yourself