Calendar sharing between users of different M365 tenants

Question

I'd like to enable a user in one M365 tenant to share his calendar with an external user in another M365 tenant (so both using EXO/M365) with EDITING rights (so not just viewing). Is this now possible between M365 tenants or is the sharing still limited to just the viewing with a 3 hour sync window? I tried running the powershell cmdlet  "add-mailboxfolderpermission -identity ******@domain.com:\calendar -user ******@otherdomain.com -accessrights editor" which works but the external user still has no edit rights. Is there any additional step to be done or is it not possible?

Thanks

Answer 1

Dear Luke

Good day! Thanks for posting in the Microsoft Community. We'll be happy to help!

First of all, we regret for the inconvenience caused to your work. Based on your description, I have a general understanding of your question, to enable a user in one M365 tenant to share their calendar with an external user in another M365 tenant with editing rights, you need to ensure that external calendar sharing is enabled in the Microsoft 365 admin center. Here are the steps to follow:

1. Enable External Calendar Sharing:
   • Go to the Microsoft 365 admin center.
   • Navigate to Settings > Org Settings.
   • On the Services tab, select Calendar.
   • On the Calendar page, choose whether you want to let users share their calendars with people outside of your organization who have Microsoft 365 or Exchange
2. Invite External Users:
   • Once sharing is enabled, calendar owners can extend invitations to specific users. They can do this through Outlook Web App by sharing their calendars with anyone inside or outside the organization
3. PowerShell Command:
   • The PowerShell command you used (add-mailboxfolderpermission -identity ******@domain.com:\calendar -user ******@otherdomain.com -accessrights editor) is correct for granting editing rights. However, please kindly ensure that the external user has accepted the invitation and that the sharing settings are correctly configured in the admin center

For your reference: Share calendars with people outside your organization - Microsoft 365 admin | Microsoft Learn

If the external user still does not have edit rights, double-check the sharing settings and ensure that the external sharing policy allows for the level of access you are trying to grant.

Meanwhile, if you still need further help or I misunderstood your meaning, please kindly correct me and share more details with me so that I can do more research and tests, thanks.

Thank you in advance for your understanding. Your patience and cooperation will be highly appreciated. I hope for all the best!

Sincerely

Kerry Chen | Community Moderator

Answer 2

Hi Kerry,

thanks for the details - I have already done everything listed (enabled external sharing in the org, invited the user, the user has accepted). The user sees the calendar in Outlook or Outlook Web App but still cannot edit the calendar. I noticed that after I ran the powershell command, the ownder of the calendar sees 2 identical users, one considered "internal" which has editing rights and the other "External" - so something isn't quite right. Any ideas?

N.B. the external user is also invited as guest in the person who sharing the calendar's tenant so this might explain why the external user is recognized as External through the invitation and internal through the powershell grant calendar permission command.

Thanks

Answer 3

Hi Kerry,

I believe after investigating further that calendar EDITING between user calendars' of different tenants is currently still not possible, only viewing is. I removed the user share and calendar, then subsequently tried to add the calendar share on the source tenant with the cmdlet but got this error:

Write-ErrorMessage : |Microsoft.Exchange.Data.Storage.RightsNotAllowedByPolicyException|The Sharing policy doesn't allow you to grant certain permissions to users on CalendarFolderfolder 'Calendar'.

The external calendar sharing policy is with full details, but no editing of course (it is not an option). The only level of access to the calendar for the user is "reviewer", not more.

As a new issue, after having removed the share access and the calendar and attempting to recreate the sharing through the usual process by inviting the external user, the external user receives the invitiation but after adding it the calendar is empty and shows no data even after waiting several hours. The share has been successfully created on the source tenant as the access level of the user is "reviewer" but the external user cannot see any data, even using webmail.

Answer 4

Dear Luke

Thank you so much for your feedback and patience! I'm sorry for the late reply!

Please first kindly refer to following information: Remove the existing permissions for the external user and then re-add them. This can sometimes reset the permissions and resolve any conflicts.

• Use the following PowerShell commands:

    Remove-MailboxFolderPermission -Identity ******@domain.com:\calendar -User ******@otherdomain.com
    Add-MailboxFolderPermission -Identity ******@domain.com:\calendar -User ******@otherdomain.com -AccessRights Editor
  

1. Check for Duplicate Entries:
   • Ensure that there are no duplicate entries for the external user in the calendar permissions. If there are, remove them and re-add the correct entry.
2. Verify Guest User Settings:
   • Since the external user is also a guest in the tenant, ensure that the guest user settings allow for the necessary permissions. You can check this in the Azure Active Directory admin center under Users > Guest users.
3. Clear Cache and Re-sync:
   • Sometimes, clearing the cache and re-syncing the calendar can help. Ask the external user to remove the shared calendar from their Outlook and then re-add it.
4. Check External Sharing Policies:
   • Double-check the external sharing policies in both tenants to ensure that they allow for the level of access you are trying to grant.

If these steps do not resolve the issue, since our forums lack relevant permissions and tools, in order to better help you and not waste more of your time, please kindly try to create a service ticket in the Microsoft 365 admin center****to support > service requests through navigation, as they have more access permissions than on this forum, and professional engineers will further help you.

Sincerely hope that your problem will be solved as soon as possible! Wish you have a wonderful day!

Sincerely

Kerry Chen | Community Moderator

Answer 5

Dear Luke

Thank you so much for your feedback and patience! I'm sorry for the late reply!

I really want to help you, and I'm consulting your thread with my team members, and I'd like to share some more specific redirect information with you, but our forum lacks relevant permissions and tools, in fact Microsoft has a separate team resource where our most valuable professional engineers and members can provide possible information for your issue, then please trust that for the issue you mentioned, they can give you more professional support. So to help you better and not waste more of your time, I highly recommend you to use your admin account to create a service ticket in the Microsoft 365 admin center****to support > service requests through navigation, as they have more access permissions than on this forum, and professional engineers will try their best to further help you.

Sincerely hope that your problem will be solved as soon as possible! Hope you all the best!

Sincerely

Kerry Chen | Community Moderator