Shared M365 calendar not refreshing in a second M365 account - any suggestions?

New Contributor


I recently shared a M365 Outlook calendar with another user (recipient) who also has a M365 account (in a different organization). They accept my shared calendar invite and they can now see my calendar in their Outlook desktop client (good). The issue we are having is that when I add an appointment on my calendar (the one that was shared) the recipient does not see the update. They tried closing and restarting their Outlook desktop but that didn't help.


I'm trying to figure out why the shared calendar is not updating on their end, any suggestions? They are running the latest version of Outlook 365 desktop. 



3 Replies

Update on this issue: about 20 hours later the change in the shared calendar now appears. Is there a way to change the frequency by which shared calendars are update in Outlook?

best response confirmed by Karen_Curtis (New Contributor)

Hi @Karen_Curtis,




Instant syncing for sharing outside your tenant isn't supported currently. While you can share in these configurations, syncing will happen periodically. There are two types of cross-tenant sharing:

  • Microsoft 365 to another Microsoft 365 user (if external sharing is enabled).

    A full shared calendar is created, but the sync will happen approximately every three hours. Instant syncing will eventually be enabled for this setup.

  • Microsoft 365 to an user. If external sharing is disabled, sharing to another Microsoft 365 user also falls into this group.

    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 or an Microsoft 365 user, the sync will happen approximately every three hours.

@boneyfrancis thank you so much, this is exactly the information I was looking for!