This video below pretty much sums it all up; you can utilize email reverse lookup sites as they are extremely powerful. The have extensive databases and tools to find the information that you are looking for.
Like I said in the main post, you can try the free methods of reverse email lockup but they will not be as effective as a paid service, you may get many duplicates, wrong or outdated information or no information at all. They also have very limited resources and usually do not have all of the most recent information from all the big email providers, even worse if the person you are looking for has either opted out of directories (mush like you can do with your phone number) or if they are with a “smaller” email provider will make it very difficult to find an email address.
But don’t fret companies are set up out there to find this information for you for a small nominal fee. It all depends on how much you need the information really, you can find out more here.
Here is a related video for those of you (like me) who are “visual learners”:
