At the moment, you can only have one email per account or user. Having that said, you can always use a + sign in your email to create another account.
Some mail servers support adding an arbitrary suffix introduced by a ‘+’ sign. The email address will be different but still reach you. For instance, your-email+client1@gmail.com and your-email+client2@gmail.com will all be redirected to your-email@gmail.com.
If you’re with office 365, you can refer to this guide