Any email validation service should be doing checks to make sure email addresses aren't fakes. Want a simple example of this? How many times has firstname.lastname@example.org tried to signup to your service?
A fake check is not only about looking for obvious fake emails, but also about looking out for disposable emails.
You do not have time to keep up to date with all the temporary email services out there, so make it our job to identify them. We're constantly updating our database with emails we identify as fakes.