How to fix syncing lag relating to Outlook calendar shared with external organization?

Rudy Hamid 20 Reputation points


  • I have 2 organizations (companies/Org) with their own email domain name
  • Aim: I want to share a calendar from a user in Org A to a user in Org B and allow Org B user to add, remove, edit calendar items
  • I've been able to do so under Sharing Permissions
  • BUT when viewing the calendar from Org B user point of view,
    • Not all calendar items are present
      • And when Org B user adds a calendar item, it does not appear from Org A user's point of view even after a day has lapsed
  • Each organization had procured Microsoft 365 from different authorised vendors (some of my colleagues suspect that this impedes syncing?)

Troubleshooting Attempted:

  1. In Outlook calendar, I have tried going to "Send / Receive" and clicking on "Send/Receive All Folders" and "Update Folder". After the progress bar has completed, the issue persists.
  2. In both organisations admin center, I've allowed calendar sharing permissions to external organisations.

Any help or advise is greatly appreciated! Thank you!

Microsoft 365
Microsoft 365
Formerly Office 365, is a line of subscription services offered by Microsoft which adds to and includes the Microsoft Office product line.
4,336 questions
Microsoft Exchange Online
A family of Microsoft email and calendar products.
3,411 questions
Microsoft Exchange Online Management
Microsoft Exchange Online Management
Microsoft Exchange Online: A Microsoft email and calendaring hosted service.Management: The act or process of organizing, handling, directing or controlling something.
4,378 questions
Microsoft Exchange
Microsoft Exchange
Microsoft messaging and collaboration software.
459 questions
0 comments No comments
{count} votes

Accepted answer
  1. Jarvis Sun-MSFT 10,181 Reputation points Microsoft Vendor

    Hi @Rudy Hamid ,

    Welcome to our Q&A forum!

    Based on your description, it seems that you have already taken the necessary steps to enable calendar sharing between two different Microsoft 365 tenants. However, it is possible that the issue is caused by the fact that each organization has procured Microsoft 365 from different authorized vendors.

    I would recommend checking if the Microsoft 365 subscriptions of both organizations are compatible with each other. If they are not, it could be the reason why the calendar items are not syncing properly.

    You can also try synchronizing users in multitenant organizations in Microsoft 365. This will allow you to sync users and groups to other tenants, which could help resolve the issue. You can follow the steps outlined in this article to synchronize users in multitenant organizations.

    If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment". 

    Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.

0 additional answers

Sort by: Most helpful