Before your set up Mail service for the first time, do the following.
Decide whether to use POP, IMAP, or both for accessing mail.
If your server provides mail service over the Internet, obtain a registered domain name.
Determine whether your ISP will create your MX records or whether you’ll create them using your own DNS service.
Identify the people who will use mail service but who don’t have user accounts in a directory domain accessible to mail service. Then create user accounts for these mail users.
Determine your authentication and transport security needs.