"mac" as in a Mac computer? It has nothing to do with the computer, it's determined by the particular email service. Search
email settings provider
where "provider" is your email provider name, like gmail or hotmail. You'll get 3 lists - POP3, IMAP and SMTP. Each will have addresses, port numbers and security (login) settings. Set yourself up that way.
POP3 and IMAP are incoming email; each works differently. Most people today use IMAP, but I think that's because it's the default, not because people understand the differences. (Reading the Wikipedia articles on both may lead you to decide to use the one better suited to your needs, rather than the one most people use.) SMTP is ONLY outgoing email, and will have no effect on what you receive.