Usually, UNIX / Linux user account used as email account. There are other ways like use sql / ldap backend to store username and password for email server which requires additional configuration and options. You can simply create user account using useradd command and modify account using usermod command. To delete user account use userdel command. Here is command to add a new email user account:
You need to configure IMAP / POP3 along with Postfix to send and recive emails from Outlook or Thunderbird.
useradd -s /sbin/nologin username