Outlook.com versus Outlook Web App in Office 365


Microsoft’s marketing for cloud offerings is changing often and sometimes can be confusing to customers – like me. Often, there are Microsoft consumer brands that sound line enterprise brands, but are two different products behind the scene. One place this confusion is prominent lately is in cloud based email clients. There are two different web email clients, one focused on consumers, basically advertising funded, Outlook.com and one sold to businesses, Outlook Web App in Exchange Online as part of the Office 365 for Business suite.


Outlook.com is the latest version of the Hotmail product for consumers. It has 400 Million users and is supported by advertising like GMail. You can login to the service with your Microsoft Account at http://outlook.com. In my experience, I’m redirected from that address to a web address in the mail.live.com domain.


Outlook Web App in Office 365

Outlook Web App used to be called Outlook Web Access and is sometimes abbreviated OWA (commonly pronounced O-W-A or Oh-Wa.)  It is a web client for Exchange Server or Exchange Online. The web client has been improved with each successive version of Exchange and the latest is shipped with both Exchange Server 2013 and Office 365 for Business Exchange Online.



Try not to confuse Outlook Web App with Office Web App, which may be rebranded Office Online. This second OWA is sometimes referred to as WAC for Web Application Companion for example see this OneNote help page or this slide deck from MCA,MCM and MVP Wictor Wilen.

Office Web App is a service that provides web clients for popular Microsoft Office Desktop products, like Word, Excel and PowerPoint. Like Outlook Web App, it’s available in an on-premises version, complimentary to SharePoint and a cloud version as part of Office 365 for Business.


While both Outlook.com (think Hotmail) and Mail.Office365.com (think Exchange) are Microsoft Web Based Cloud Email Offerings, they are two different products. Either one can be useful to you when you keep in mind who is targeted by the platforms. If you’re looking for a Yahoo Mail or GMail replacement, you’re probably going for Outlook.com. If you’re looking to migrate from Exchange Server or Lotus Notes Servers running at your business to the cloud. Think of Office 365 for Business Exchange Online at mail.office365.com


Microsoft moves closer to launching free ‘Office Online’, Feb 10, 2014, Mary Jo Foley, ZDNet

How to Survive the Hotmail to Outlook.com Transition, May 2013, http://blog.gcflearnfree.org/


Technical Background

I can’t find much technical reference material that I can link to which highlights the backend differences of Outlook.com versus Outlook Web App. My guess is that there are two different teams working on the two different products. Also, outlook.com should have been engineered from the ground up to be cloud capable. On the other hand, Outlook Web App was developed originally to be an on-premises solution and retains the legacy of that design.

Here’s one peek behind the scenes which is telling on the legacy of the two applications. When I view the HTML source behind Outlook Web App in Office 365, I see 61 references to Exchange.


When I do a similar look behind the code of Outlook.com, I don’t see any exchange references, but there are 9 to Hotmail.


  1. Office 365 all the way for me.

  2. Hey, I just seen that sometimes this website shows a 404 server error message. I figured that you would be keen to know. Best wishes

    • I use Microsoft Office home, which runs outlook.office.com
      Since 2 days however it comes up with [object ReadableByteStream]
      And I have no idea how to get back were it would go direct to my email.
      Anyone who could advise and help solve this asap

      Have to give you alternative email address

      • Sounds like it could be an issue with the browser. I would try some of the troubleshooting steps suggested here: https://www.lifewire.com/check-service-status-outlook-1170646

        • Hi Tom,

          Still have the same problem, it is still not working get the same message [object ReadableByteStream] have no idea what to do,

          From Home Office, I normally get the to press Linkedin and this say working and I get into my email.
          Now I get the above message and Linkedin stops, This is becoming an urgent issue issue. This is my business email

          • Sorry to hear that. If this is a business account, I can recommend going to https://admin.microsoft.com and selecting the Need help? option on the lower right. If there isn’t a documented solution, you can also contact support through that experience.

  3. I wondered what OWA stud for and now I know.

  4. I agree Jon 365!

  5. Thanks for clarifying!

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