Trouble with E-mail not showing up on Mac and IPad

Hello all, I have a friend who I am trying to help with e-mail. This person is wanting to get e-mail on both the Mac book and the IPad. However, when he attempts this, the E-mail only goes onto the IPad and not onto the computer. I have been unable to find a setting for him to keep the mail on the server to be picked up by the computer. Thanks for any help Andrea Barker