Internet Calendar Subscriptions – Part 1

This post is coming to you courtesy of Can Comertoglu, our Outlook PM in charge of our Internet Calendaring experience.  The new Internet Calendar functionality falls under the Sharing experience for Outlook 2007, so I've asked Can to take a few posts and discuss it with all of you here on the Search.Subscribe.Search blog.  I encourage everyone to ask questions at the end of each post; we'll aggregate them together and do another Q&A soon.

Can, take it away...

Outlook 2007 introduces Internet Calendar Subscriptions, the ability to download Internet Calendars (.ics files) into Outlook and receive updates to the calendar content automatically. While Internet Calendars can be downloaded into Outlook without the subscription functionality, the dynamic nature of the subscription-based calendars makes them a compelling solution for online content providers to provide rich content to their users.

When an Internet Calendar is downloaded using the subscription functionality, the calendar is read-only and bound to the original Internet Calendar on the server. This dynamic binding allows updates to be received by the client every time the original calendar changes. Internet Calendars that are downloaded into Outlook without the subscription functionality are not ready-only and can be modified in Outlook. However, the downloaded calendar will not be updated automatically when the original calendar is changed.

Subscription-based Internet Calendars use the WebCal protocol (webcal://), which is a derivative of the http:// protocol and is used to create the subscription binding.

Internet calendars can be brought into Outlook for subscription in three ways:

  1. Clicking a “webcal://” link in a web browser: When you click on a webcal:// link, Outlook displays the confirmation dialog box as below, and clicking yes creates the subscription binding.  This is the easiest way to subscribe to calendars found in online Internet Calendar Directories such as

  2. Subscribing via Outlook Account Manager: The alternative option is to create the binding manually by going into Account Manager in Outlook (Tools->Account Settings) and switching to Internet Calendars tab as shown in the picture below. Here you can both change the settings on existing subscriptions, and add new subscriptions by clicking “New”.  Once you enter the calendar address in the dialog box, Outlook will create the subscription binding.

  3. Subscribing via a Sharing Message from another Outlook user: In subsequent posts, I will be talking about publishing Internet Calendars from Outlook 2007. After publishing calendars, users can send Sharing Messages to the users that they would like to share their calendar with. Recipients can subscribe to those published calendars from within Outlook, creating a seamless publishing/subscribing experience.

Comments (31)

  1. AdamB says:

    1. "However, the downloaded calendar will not be updated automatically when the original calendar is changed." So how do they get updated?

    2. Can you compare and contrast the functionality offered here vs. that of Outlook Calendar Sharing in an Exchange Environment?

    3. Perhaps answered by (2), but will this work for Free/Busy information (i.e., is it queried when you go to schedule an appointment with someone).

    4. What scenarios do you see this primarily used in? For people to organize meetings with each other? For groups to share a common "project" calendar? Or for more static things like the Bulls calendar example shown?

    5. Have you looked at using RSS as a transport mechanism for this information? I think there is a service called that does this. RSS to me seams like a natural way to syndicate this calendar information. If you have looked at it, what was the decision to not go in the RSS direction?

  2. Charlie Wood says:

    Will Outlook 2007 support authentication (basic or digest) or encryption (SSL/HTTPS) for Internet Calendar Subscriptions?



  3. Antoon says:

    I suppose this is not available for Outlook 2003?

  4. There is a good post on internet calendars written by Can Comertoglu, Outlook PM on Michael Affronti’s…

  5. John Berg says:

    What will be the link (if any) to Exchange server / Outlook Web Access? I guess what I am trying to ask is if calendars added to outlook will be accessable in Outlook Web Access?


  6. Kerem Cimen says:

    Would Microsoft provide tools and code samples for generating webcal protocol?

  7. Sal M says:

    SO… subscription only, no built-in publishing?  Or is that in Part 2 🙂

  8. Internet Calendar Publishing in Outlook 2007

    I talked about Internet Calendar Subscriptions in Outlook…

  9. Why a new, fake protocol?

    What was missing from HTTP?

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