I haven't migrated from Netscape to Outlook so I can't help Rev, however I'll attempt to explain why you might want Outlook. Outlook 2003 is a very good program. Over the years I've gotten a ton of spam and I've never gotten a virus. I use a plugin called Qurb to filter all emails not from a whilelisted address into a secondary folder where I have the preview window disabled. By never opening or previewing suspect emails I'm less likely to get a virus.
Another cool feature is the desktop alert. It shows a preview in the bottom right corner of the screen as new emails arrive. I use this feature to avoid bringing Outlook to the foreground unless the email seems important. This allows me to keep more of my attention focused on my work.