Helping people with computers... one answer at a time.
Even though they share similar names and do similar things, Outlook, Outlook Express, and Outlook.com are actually not related to each other at all.
I see I have Outlook Express on my machine for email. But I also see references here and elsewhere to just "Outlook," and now Outlook.com. Are those just other names for the same thing? If not, how do all these "Outlooks" relate to each other?
The short answer is they don't. Not at all. They essentially have only two things in common. They're all related to email and they all have the word "Outlook" in their names.
And that's pretty much where the similarity ends.
It's unfortunate too because lots of people infer from the names that Outlook Express is some kind of "Outlook Lite" and that Outlook.com has something to do with one or the other or both. That's simply not the case at all. They're completely separate from each other.
Outlook Express was:
Free - It was included on most Windows installations prior to Windows Vista and came with Internet Explorer versions 6 and earlier.
An internet mail reader - POP3, IMAP or Hotmail accounts.
An internet news reader - NNTP, as used on Usenet and other internet news servers.
A contact list manager - Although aimed primarily as a way of managing contacts specifically for mail and news.
I say "was" because Outlook Express has been DISCONTINUED.
Outlook Express has been formally discontinued by Microsoft and won't be found in Windows versions begining with Vista. In fact, Outlook Express will not run in Windows 7 and presumably will also not run in Windows 8.
My experience answering questions on and trying to help people with Outlook Express is that it is long past time to move on and select another email program. I hear of more email lost because of issues with Outlook Express than with any other email program.
Not free - It's included in the Microsoft Office product.
An internet mail reader - POP3, IMAP, or Hotmail accounts.
An exchange server mail reader and support all exchange server features.
A full-featured personal information manager (PIM) with address book, calendar, todo-list and more.
Extensible - Outlook can be extended via add-ins and macros.
Regularly updated and supported.
There are many more differences, of course, but those are the major ones that are visible. Under the hood, the most major difference between Outlook and Outlook Express is simply that that they share almost no code. They've come from completely different backgrounds to evolve into what they are.
Introduced in 2012, Outlook.com is:
A web-based email service that you access using your web browser.
An email domain on which you can create your own free email address, much like Microsoft's Hotmail.
An alternate user interface that you can use to access your existing Hotmail email.
Rumored to eventually replace Hotmail's user interface completely (though Hotmail email accounts will continue to work)
As you can see, Outlook.com doesn't even come close to relating to Outlook or Outlook Express is any way. The latter two are email programs that you install on your PC, Outlook.com is a website you use to access email.
The only thing Outlook.com shares with Outlook and Outlook Express is the word "Outlook", which is apparently Microsoft's generic branding for anything email-related.
Outlook Express was targeted at the home user and many people felt that it was both simple and met their needs quite nicely. Unfortunately, with it being discontinued for nearly a decade now, it's not a solution that you should choose if you're setting up something new. In fact, it's something that I strongly suggest you move away from if you're using it today. My recommendation would be to move to a program like Thunderbird.
Outlook, on the other hand, continues to be targeted more at the business environment, email power-users, or those simply wanting all the additional features it brings. With a lot of support from third-party vendors, including things like mobile device synchronization, Outlook is even a reasonable choice for the home or casual user.
Outlook.com is totally optional. If you have a Hotmail account, you can try out Outlook.com's new user interface and see if you like it. (My experience is that you can revert back to the older Hotmail user interface if you like, but some have reported difficulty doing so, so proceed at your own risk.)
A safer way to try the new Outlook.com might be to go there and sign up for a new Outlook.com email address, leaving your existing Hotmail address out of the picture.
(This is a revision of an article originally published August 17, 2003.)
You can read more about Outlook versus Outlook Express in the Microsoft support article: Differences Between Outlook and Outlook Express.