You say that your dad is familiar with Microsoft Outlook. While Outlook isn't available on the Mac, Microsoft Entourage is. Entourage is essentially the same as Outlook, it's just been created for the Mac. They're actually going to be replacing Entourage with Outlook when Microsoft Office 2010 comes out next year.
You say that your dad has "a lot of emails using an microsoft outlook email address". I'm not exactly sure what you mean by that. Outlook doesn't have an email address exactly. Are you talking about an Exchange account, per chance? A lot of companies/schools use Exchange servers, which can synchronize with Outlook (or Entourage). Although since the release of Snow Leopard, you don't even need Entourage to connect to an Exchange server -- it comes built right in using the Mac's Mail program.