System requirements To install Mail essentials 5, which runs on Windows NT, you need: Windows NT server or Workstation Service Pack 6 Microsoft Exchange server 4, 5 or 5.5, Lotus Notes 4.5 and up, or an SMTP/POP3 mail server. Internet explorer 5 or higher installed MMC 1.2 or higher installed Microsoft Outlook 2000 OR Windows Messaging installed on the Mail essentials machine. Windows Messaging can be installed using Add/Remove programs. The mail client must be installed as the default mail client!