What does 'Enable Domain Checking' setting do?

Hi there

There is this 'Enable Domain Checking' setting under Message Settings/Email Preferences - you can have it On or Off. What does it do, exactly?

This article from wikipedia might help Email authentication - Wikipedia, the free encyclopedia but there are several methods described so that doesn't help in precisely what method is being used on the playbook.

Thanks! So, basically, this setting helps you verify the identity of email sender, right?