Calendar sharing in Office 365

Background

We're making improvements to the way that shared calendars in Office 365 sync across your applications. When all the improvements are complete, you can expect:

  • Consistent permission options when sharing a calendar.

  • An easy way to accept a shared calendar invitation.

  • That shared calendars will sync to all devices and the changes will appear right away.

These improvements are in progress and will continue to roll out over the next year. This article focuses on the changes you can see today and provides details about our future plans. We'll continue to update this article so that it always reflects the latest changes.

Is this article going to answer my question?

This article is intended for IT Administrators, to help them understand the changes that are rolling out. If you're someone who just wants to know how to share or delegate a calendar, see the following articles:

Which shared calendars are eligible for these improvements?

The improvements are rolling out only for calendars shared between people using Exchange Online. There are no changes to shared calendars when one person's calendar is hosted in Exchange on-premises.

Sharing a calendar

The first improvement is that you can share your calendar from any Outlook application, and have the same permission options on all Outlook applications. The table below shows the current state of our work to make it simple to share your calendar.

Outlook application

Can share a calendar

Consistent and simple permissions when sharing

Notes

Outlook for Windows

Simplified permissions are expected to roll out in Q4 2017 to the Monthly update channel.

Outlook for Mac

There is no timeline yet for simplified permissions.

Outlook on the web

Outlook on iOS

Outlook on Android

Calendar for Windows 10

1

1 Calendar sharing is enabled only for Windows 10 on PC. Calendar sharing won't be released for Windows 10 Mobile.

Accepting a shared calendar

The second improvement is that you can easily accept shared calendar invitations from any Outlook application, and see those shared calendars on all of your devices. The table below shows the current state of our work to make it simple to accept a shared calendar invitation.

Outlook application

Can easily accept a shared calendar

Accepting the shared calendar syncs it to all devices

Notes

Outlook for Windows

1

2

1 Calendar sharing is currently supported only for Office 365 users. Outlook.com users cannot yet accept invitations from Outlook for Windows. Calendar sharing for Outlook.com users on the Outlook for Windows application is expected to be supported in Q4 2017 for the Monthly update channel.

2 This is expected to roll out in Q4 2017 to the Monthly update channel.

Outlook for Mac

There isn't an option to accept a shared calendar invitation in Outlook for Mac, but users can add a calendar from their directory or address book. There is not yet a timeline to add an easy accept button when viewing the shared calendar invitation.

Outlook on the web

Outlook on iOS

Outlook on Android

Calendar for Windows 10

3

3 This is not yet enabled for all Windows 10 Mobile users.

Syncing and editing shared calendars

The third improvement is that you can view all of your shared calendars on any device or calendar application. If someone changes a shared calendar, all other people sharing the calendar will see the changes instantly. You'll also notice performance improvements when viewing and editing shared calendars. Using a shared calendar will be as fast and reliable as managing your own calendar.

Shared calendars sync to all devices

When you share your calendar with people today, they will enjoy the improved shared calendar experience after accepting the invitation. However, if you shared your calendar with people before these changes were enabled, they won't have these improvements automatically. To upgrade your existing shared calendars to the new shared calendar experience, follow the instructions in this section. In the future, existing shared calendars will be upgraded automatically, but there's no schedule yet for this upgrade process.

Upgrade your shared calendars so that they start syncing to mobile

This section provides instructions for how to upgrade your shared calendars so that they start syncing to your mobile phone.

Instant syncing

With instant syncing enabled, a shared calendar will reflect changes made by others immediately. Currently, not all types of shared calendars support instant syncing. The following sections cover the types of shared calendars and calendar applications that support instant syncing.

Which types of shared calendars support instant syncing?

Instant syncing is enabled only if both users are in the same Office 365 tenant, or if the calendar is shared by an Outlook.com user.

The table below provides more details on the types of configurations that support instant syncing. In the future, instant syncing will be enabled for all calendars shared among Office 365 and Outlook.com users.

Calendar owner

Shared calendar recipient

Instant syncing enabled

Notes

Office 365

Office 365
(same tenant)

Office 365

Office 365
(different tenant)

Syncing happens approximately every 3 hours.

If external sharing is not allowed for the calendar owner's tenant, it is treated like the calendar is being shared to a third-party user.

Office 365

Outlook.com or
third-party such as Gmail.com

This configuration currently generates an Internet Calendar Subscription (ICS) URL. The shared calendar recipient adds the shared calendar using the ICS URL, and the sync timing is determined by the recipient's calendar service.

For example, if the recipient is in Outlook.com, the calendar will update approximately every 3 hours. If the recipient is in Gmail.com, the calendar might be updated every 24-48 hours.

Outlook.com

Outlook.com

Outlook.com

Office 365

Outlook.com

Third-party such as Gmail.com

This configuration currently generates an Internet Calendar Subscription (ICS) URL. The recipient adds the shared calendar using the ICS URL, and the sync timing is determined by the recipient's calendar service.

For example, if the recipient is in Outlook.com, the calendar will update approximately every 3 hours. If the recipient is in Gmail.com, the calendar might be updated every 24-48 hours

Which applications support instant syncing?

Application

Supports instant syncing

Notes

Outlook for Windows

Instant syncing is expected to roll out in Summer 2018 for the Monthly update channel.

Outlook for Mac

There is no timeline yet to support instant syncing.

Outlook on the web

Outlook on iOS

Outlook on Android

Windows 10 Calendar

REST applications

Exchange ActiveSync applications

Note: Exchange Web Services (EWS) API will not support instant syncing.

To use instant syncing, your shared calendar must be enabled for instant syncing, and your calendar application must be updated to take advantage of this feature.

If your shared calendar is enabled for instant syncing, and you're viewing it on Outlook on the web, Outlook for iOS, or Outlook for Android, you have the new sync experience. If you're viewing that same calendar on Outlook for Windows or Outlook for Mac, you still have the old sync experience. Currently, for the same shared calendar, changes might appear faster in Outlook on the web, iOS, or Android than on Outlook for Windows or Outlook for Mac.

Technical details of the shared calendar improvements

This section describes how these improvements were accomplished, and what changed in the architecture of shared calendars in Office 365.

Terminology

Here are some terms that we'll use in the below explanation:

  • Shared calendar: A calendar shared with view, edit, or delegate permissions

  • Owner: The person from whom the calendar is shared

  • Recipient: The person to whom the calendar is shared

  • Old model: The old behavior of shared calendars

  • New model: The new behavior of shared calendars

Summary of differences

The improvements are only rolling out for calendars shared between users in Exchange Online There are no changes to shared calendars when one of the users is hosted in Exchange On-Premises.

Attribute

Old model

New model

How the shared calendar is stored

An entry (similar to a hyperlink) is stored in the recipient's mailbox. The entry points to the owner's mailbox but doesn't store any calendar data in the recipient's mailbox.

A new calendar is created in the recipient's mailbox, and this calendar contains a copy of the owner's calendar (starting one year prior to date of acceptance).

How recipient accesses the shared calendar

Reads and writes directly from the owner's mailbox.

Reads and writes from the local copy of the shared calendar stored in the recipient's own mailbox.

How the shared calendar syncs changes

The application periodically polls the owner's mailbox for changes and syncs them down.

The service instantly syncs changes to the recipient's local copy. This triggers a push notification to the application which syncs down the changes instantly.

Which applications the recipient can use to access the shared calendar

  • Outlook for Windows

  • Outlook for Mac

  • Outlook on the web

  • Outlook for Windows

  • Outlook for Mac

  • Outlook on the web

  • Outlook for iOS

  • Outlook for Android

  • Calendar for Windows 10

  • All REST & EAS applications

Is my shared calendar on the old model or the new model?

Users that accept a new shared calendar invitation from Outlook on the web, iOS, or Android will automatically start using the new model of calendar sharing.

The easiest way to check if you have the improvements (meaning you’re on the new model of calendar sharing) is to check if the shared calendar appears on your mobile phone. If it does, the shared calendar is already upgraded to the new model.

If you prefer to use MFCMapi, you would need to confirm that the following is true:

  • A local folder for the shared calendar appears in the Calendar subtree.

  • An entry exists in the Common Views > Associated Contents table. The entry’s named prop name is SharingCalendarGroupEntryAssociatedLocalFolderId, and it will point to the ID of the local shared calendar folder.

How do I upgrade an existing shared calendar to the new model?

If you want your shared calendars to benefit from these improvements, you just need to recreate the shared calendar by doing the following:

  1. Ask the owner to re-share the calendar to you. They can do this from any Outlook application, even Outlook for iOS or Android!

  2. Accept the shared calendar invitation using Outlook on the web, iOS, or Android. It's important that you accept the invitation from Outlook on the web, iOS, or Android. If you accept the invitation using Outlook for Windows or Outlook for Mac, the shared calendar will not be enabled with these improvements. You don’t need to remove any existing shared calendars before re-accepting.

You can accept shared calendars in one of two ways:

  1. Receive a sharing invitation via email and click the Accept button.

    To add a shared calendar via the new model, you must accept the email invitation from Outlook on the web, iOS, or Android. Accepting from Outlook for Windows or Outlook for Mac won't upgrade the calendar to the new model.

  2. Open the calendar by searching the directory for the calendar owner. Opening a shared calendar from the directory or address book will add the calendar via the old model of sharing.

In the future, shared calendars will upgraded to the new model regardless of which method you choose.

Methods for syncing shared calendars

This section discusses where and when instant syncing occurs in the current state of our progress. First, we'll list the types of syncing that exist for shared calendars in the new model:

Update method

How are changes synced

Supported calendars (currently)

Instant updates

Changes sync instantly. This applies to calendars shared between users in the same Office 365 tenant, or shared from an Outlook.com user.

  • Shared from an Outlook.com user to an Outlook.com or Office365 user

  • Shared directly between Office 365 users in the same tenant

Periodic updates

Changes sync periodically (within 3 hours in most cases). Recipients won’t see changes on a shared calendar immediately, but the copy will be updated every few hours.

  • Shared indirectly between Office 365 users in the same tenant (via default user permissions, or via a security group with more than 100 members)

  • Shared between Office 365 users in different tenants, with external sharing enabled

ICS subscription

An Internet Calendar Subscription (ICS) URL is generated when the calendar is shared. The recipient can use this URL to add the shared calendar to any calendar service that they use. With ICS URLs, the recipient’s calendar service chooses when to sync the calendar to receive new updates. If the recipient is an Outlook.com user, the sync will happen approximately every 3 hours.

  • Shared between Office 365 users in different tenants, with external sharing disabled

  • Shared from an Office 365 user to an Outlook.com user

  • Shared from an Office 365 or an Outlook.com user to someone using a third-party calendar service, such as Gmail

Sharing within the same tenant

There are three ways that a user can be granted access to a shared calendar:

  1. Direct permissions: The calendar owner shared directly to the recipient, and the recipient is listed individually in the calendar owner's permissions list.

  2. Group permissions: The calendar owner shared the calendar to a security group, of which the recipient is a member.

  3. Default permissions: The calendar owner set a default permission for users in the same organization, and the recipient has access via the default permission.

Currently, instant syncing is only enabled for direct permissions and for group permissions if the group size is under 100. In the future, instant syncing will be enabled for all three of the above permission types.

Sharing outside a tenant

We do not yet support instant syncing for sharing outside your tenant. While you can share in these configurations, syncing will happen periodically. There are two types of cross-tenant sharing:

  1. Office 365 to another Office 365 user (if external sharing is enabled)

  2. Office 365 to an Outlook.com user. If external sharing is disabled, sharing to another Office 365 user also falls into this group.

For option 1, a full shared calendar is created, but the sync will happen approximately every 3 hours. Instant syncing will eventually be enabled for this setup.

For option 2, an ICS URL is generated when sharing, which the recipient can use to add to any calendar service. With an ICS subscription, the recipient’s calendar service chooses when to sync the ICS subscription to receive new updates. If the recipient is an Outlook.com or an Office 365 user, the sync will happen approximately every 3 hours.

Sharing outside Office 365 and Outlook.com

Sharing to a user on an external service such as Gmail is a different kind of calendar sharing. In these scenarios, an Internet Calendar Subscription (ICS) URL is generated that links to the owner’s calendar. Recipients can use this URL to view the calendar in a web browser, or add it to their own calendar service by adding an internet calendar using the ICS URL. With ICS subscriptions, the recipient’s calendar service chooses when to sync the ICS subscription to receive new updates. If the recipient is an Outlook.com user, the sync will happen approximately every 3 hours. If the recipient is using another calendar service, such as Gmail.com, the sync might not happen as frequently.

What functionality is different in new model shared calendars?

Reminders

In the first phase of calendar sharing improvements, recipients will always see “Reminder=None” for shared calendar items, regardless of the true reminder value for an item. If a recipient with edit access tries to change the reminder on an shared calendar item, the new reminder value will be locally saved only for the recipient and not for the owner.

How did reminders work in the old model: In the old model of sharing, the recipient accessed the calendar owner’s mailbox directly. Therefore, when they viewed a calendar item, they saw the same reminder value that the owner saw. Outlook clients knew how to detect which calendars were shared calendars, so they did not show pop-up reminders for any shared calendar items.

Why did behavior change in the new model: In the new model of sharing, the shared calendar is stored locally in the recipient’s mailbox. Therefore, when mobile applications sync down these shared calendars, they might not always check whether it’s a shared calendar. In those cases, we found that when we synced down the true reminder value to a recipient who was using a third-party EAS or REST client, the recipient was flooded with reminders for other people's meetings. We're investigating ways to improve reminders experience without breaking third-party clients.

Below is an example of how reminders differ:

Scenario

Reminder value seen by the owner

Reminder value seen by the recipient in the OLD model of sharing

Reminder value seen by the recipient the NEW model of sharing

Calendar owner creates a meeting on the shared calendar with a 30 minute reminder

30 minutes

30 minutes

None

Calendar recipient creates a meeting on the shared calendar with a 30 minute reminder

30 minutes (and attendees receive a meeting with a 30 minute reminder)

30 minutes

None

Calendar recipient edits an existing meeting on the shared calendar to have a 60 minute reminder

60 minutes (if edited via OLD model)

30 minutes (if edited via NEW model)

60 minutes

60 minutes (recipient would receive a popup 60 minutes prior to meeting start)

Changing permissions

If the owner uses Outlook on the web, iOS, or Android to change the permissions, this will trigger an immediate re-sync of the recipient’s copy of the calendar to the new permission level.

If the owner uses another application to change the permissions, the calendar will be re-synced sometime in the next few hours, but it will not happen immediately.

Removing permissions

If the owner removes someone’s permissions on the calendar, this will be detected within a few hours and one of three things will happen:

  1. If the recipient is in the same organization, and the calendar owner has the My Organization (default) user set to any permission other than None, the recipient’s calendar will be updated to reflect the default user’s permission level. The shared calendar will remain on the new model, but it might have a different permission level.

  2. If the recipient is in the same organization, and the calendar owner is not sharing their calendar to the My Organization (default) user, then the shared calendar will be removed from the recipient’s mailbox. The recipient will no longer see the shared calendar in their calendar list.

  3. If the recipient is in a different organization, the shared calendar stops syncing but is not removed.

Delegated meeting messages

Delegates have always been able to view delegated meeting messages from their mobile phone because the invitations are received in their inbox. However, in the past, delegates did not have any indication whether the meeting invitation was for them or for their manager. To better support this scenario, Outlook for iOS and Outlook for Android have added UI to make it clear for whom the meeting invitation is intended.

Third-party clients

  • In EAS clients, recipients with read-only permissions will see the option to create a meeting or respond to a meeting on that read-only calendar. Doing so will save locally to the client's cache, but the changes are rejected by the server. The recipient's changes will not be reflected in the owner's calendar because they do not have edit permissions. This issue occurs because EAS clients do not differentiate between read-only versus read-write permissions on shared calendars, and treat all calendars as editable.

  • Some third-party clients have client-side logic to always add the current user as an attendee of meetings. Therefore, if you’re using the native calendar apps on your phone and viewing a meeting on someone else’s calendar, you might see yourself in the attendee list. This only occurs if you’re viewing the calendar on third-party calendar applications – when you view the same meeting on Outlook for iOS or Outlook for Android, you will not see yourself on the attendee list.

  • We do not support the shared calendar improvements for EWS-based clients, so you will not see your shared calendars in any calendar application that uses EWS, such as Mac OS X.

    Notes: 

    • Outlook for Mac uses EWS and shows legacy shared calendars.

    • We are currently in the process of blocking shared calendars in EWS, so you may see some shared calendars in Mac OS X but they will no longer be shown in the next few weeks.

FAQ

  1. I don’t want my users’ calendars to sync to mobile phones. What settings can I use to disable this?

    We don’t have any plans to allow the shared calendar improvements to be disabled for tenants.

  2. My users are concerned about data usage when shared calendars sync to their mobile phones. What should I tell them?

    If you deselect the shared calendar in the calendar list, Outlook for iOS, Android, and Windows 10 Mobile will not sync the deselected calendars. Most mobile calendar applications should also follow this behavior.

  3. Does this also apply to resource calendars?

    Any calendar that can be shared is eligible for these improvements. If you share your own calendar, a shared mailbox calendar, or a resource mailbox calendar, and the recipient accepts using Outlook on the web, Outlook for iOS, or Outlook for Android, they will start seeing these improvements.

    However, for resource mailboxes in particular, there are some inconsistencies with the way that permissions show in the Outlook permissions list compared to the Admin Center’s permissions list. We're working to make the permissions show consistently. However, the shared calendar functionality works as detailed above for resource mailbox calendars, and the recipient will be able to see the resource calendar on their mobile phone.

  4. Do you now support sharing a calendar to Office 365 groups?

    Not yet, but it’s high on our list! You can currently only share calendars to individual users or to security groups.

Summary of experiences across clients

Below is the summary of the current state of the calendar improvements. Timelines listed below are subject to change.

Promise

Web

Windows*

Mac*

iOS

Android

Windows 10 Mobile

Share my calendar with simplified permissions

Monthly channel:
Q4 2017

Semi-annual channel:
Summer 2018

No timeline yet

Accept a calendar so it’s on the new model

Monthly channel:
Q4 2017

Semi-annual channel:
Summer 2018

No timeline yet

Q4 2017

Sync instantly via the new model

Monthly channel:
Summer 2018

Semi-annual channel:
Early 2019

No timeline yet

*Applies only to subscription customers.

Related Topics

Share your calendar in Outlook on the web for business
Calendar delegation in Outlook on the web for business
Manage someone else's calendar in Outlook on the web

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