I've received a couple of email from a person , and yahoo call it domain-keys! How could I be sure it is real?

Question

This email have a form like this : (name of the person)@gmail.com . could it be a personal email or a third person who pretend to be the real person or is it some sort of business?

Answer 1

This is a security mechanim built by Yahoo.
Domainkeys verifies that the domain from which the email was sent, is actually correct/valid and also that it came from where it claims it did.
This is to eliminate spam !

Answer 2

Its to prevent spam and it tells you if the mail has come from a yahoo account.

However @gmail.com is google so I dont know why it would have Yahoo Domain Keys so if it does it might be a fake.