Exchange Online shared calendars on mobile devices

Hi Mike,

This is part of the shared calendar improvements we are enabling & discussed during last year's Ignite conference that Vasil linked to. These improvements address a long-standing request from users to sync Office365 shared calendars to mobile phones (iOS UserVoice, Android UserVoice). We started slowly enabling this for users at the beginning of this year.

In the first iteration, newly accepted shared calendars would sync to mobile phone if the calendar was shared & accepted from Outlook on the web. In the next update, calendars could be shared from any Outlook client, and as long as the users accepted in Outlook on the web, the newly accepted shared calendar would sync to mobile.

However, it's possible to grant calendar permissions from Outlook on Windows or Mac without a sharing invitation being sent to the users. When we started releasing these improvements, many users pointed out that they "accept" shared calendars by opening the calendar in Outlook (rather than accepting a sharing invitation). So we implemented an experimental update that allowed a calendar to be accepted from Outlook on the web or Windows, using either the accept button or by opening the calendar.

This expermental update turned out to be the most noticeable difference for users like yourself. The feedback has mostly been that if I open a calendar for which I don't have direct permissions (e.g. viewing a calendar of someone in your organization with the default user permissions), then we shouldn't sync those calendars to mobile phones. However, users did want calendars to sync to mobile phones if they're opened a calendar for which they've been granted individual permissions.

To support that user feedback, we have temporarily disabled the "open calendar" update, and we're working on adding a check to determine if the user who is opening the calendar has individual permissions to the calendar. So, the current state is that only calendars accepted in Outlook on the web from a sharing invitation will sync to mobile. (However, soon Outlook on iOS and Android will also support accepting invites!)

This should hopefully explain why you see some of your colleagues' calendars on your mobile phone - if you opened a calendar in the past week or two, it was considered "accepting" the calendar and it started sync'ing to mobile phones. You can use Outlook on the web, iOS, or Android to delete the calendar, and at this point, the calendars won't re-appear even if you re-open them from Outlook.

Hope that helps explain the issue you noticed!