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User A Update meeting invitations attendees but User B meeting show cancelled

Jero Cheng 170 Reputation points
2025-08-18T07:55:18.91+00:00

HI All

I have a weird question about Outlook meeting invitation.

User A create a meeting, and sent the meeting invitation using [Send As] (send as a share mailbox: ******@testing.com )  to User B , C , D, E, F few months ago. (All of them are company staff in same O365 talent)

 

Today user A sent an update about this invitation (send as a share mailbox: ******@testing.com ), the update only added and removed some attendees ,no other change.

 

User C and D leaved company ,so User A removed C and D , and add new attendee G and H

 

User A said that the update was "sent to only added or deleted attendees "only.

 2025-08-18 15_51_08-Ask a question - Microsoft Q&A — Mozilla Firefox

 ***User B has delegated his mailbox and share his calendar to D and G

 

User B report that this meeting in his calendar is showing [Cancelled] ,while E and F has no change (calendar show the meeting correctly) ,G and H received the invitation successfully.

 

I trace "mail flow" ,from "******@testing.com" to User B.

 2025-08-18 15_51_12-Ask a question - Microsoft Q&A — Mozilla Firefox

We can see the invitation was somehow dropped with this error.

 

Reason: [Stage: DeliverPreDelivery];StoreDriver.Rules; message is deleted by mailbox rules

 

If I trace the same mail flow from "******@testing.com" to User E and F,there is no result about this invitation. That mean the update was only "sent to only added or deleted attendees ".

 

For further checking,I trace the mail flow from User G to B 

 

We can see most of the invitation from User G to B was failed,with same error.

 

*User B is the only attendees in these invitations.

 

Reason: [Stage: DeliverPreDelivery];StoreDriver.Rules; message is deleted by mailbox rules

 2025-08-18 15_35_15-Ask a question - Microsoft Q&A — Mozilla Firefox

 

But User B calendar has show the above meeting correctly.

 

I check User B mailbox permission (calendar) with Power-shell.

The delegation's of User B like below.

 2025-08-18 15_51_23-Ask a question - Microsoft Q&A — Mozilla Firefox

The problem look weird.I Google the error message and found some info.

https://www.reddit.com/r/exchangeserver/comments/p9bv74/meeting_invitation_emails_not_received_by_one/

 

I would like to know what is the root cause of this error and the solution.

Please kindly help

 

Thanks.

Outlook | Windows | Classic Outlook for Windows | For business
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Accepted answer
  1. Kristen-L 2,400 Reputation points Microsoft External Staff Moderator
    2025-08-18T18:02:39.7033333+00:00

    Hi @Jero Cheng,

    Good day! Thank you for reaching out to Microsoft Q&A forum and sharing the detail. 

    1. The pop-up window shows that User A chose to "Send updates only to added or deleted attendees", not to all attendees. This explains why User B didn’t receive a direct update.
    2. The Message Events table shows that the update email to User B was deleted by mailbox rules. That error [Stage: DeliverPreDelivery];StoreDriver.Rules; message is deleted by mailbox rules means that User B has a rule in place that automatically deletes certain meeting updates - possibly triggered by sender, subject, or other criteria.
    3. Delivery failures: Each session represents an attempt to deliver the meeting update email to User B. All of them failed the same error.

    As a result:

    • The message reached the mailbox server, but before delivery, it was intercepted and deleted by a mailbox rule.
    • These rules are typically set by the user in Outlook or via PowerShell and can automatically move, delete, or forward emails based on conditions like sender, subject, or type.

    Impact:

    • Since the update email was deleted, Outlook couldn’t process it properly.
    • This can cause the meeting to appear cancelled or missing in the calendar.
    1. Calendar permissions (PowerShell Output)

    Here’s what each permission level means and how it might affect meeting behavior:
    User Access Rights Meaning
    Default AvailabilityOnly Anyone in the org can only see free/busy info, not details.
    Anonymous None External users have no access.
    User K, D, G Editor Can create, modify, and delete items in the calendar.
    Delegate Editor Full editing rights; can act on behalf of User B.

    This indicates that:

    • Delegate has Editor access, meaning they can accept/decline meetings, modify calendar entries, and possibly trigger rules that affect meeting invites.
    • If Delegate or User K/D/G has mailbox rules set up (especially if they manage User B’s calendar), they might be unintentionally deleting or modifying meeting updates.

    Here’s why this happened:

    • User A choose "Sent only to added/removed attendees".
    • Deleted by User B’s mailbox rules, possibly due to delegation or filtering.
    • Not visible to User B, causing Outlook to mark it as Cancelled.

    Here're suggestions you can try to fix it:

    1. Check User B’s mailbox rules:

    • In Outlook Classic: File > Manage Rules & Alerts
    • Look for any rule that deletes or moves meeting invites.

    2. Review delegation settings:

    • Ensure that delegates (like D and G) aren’t unintentionally modifying or deleting invites.

    3. Resend the meeting update to all attendees:

    • Choose “Send updates to all attendees” to reset the status for everyone.

    I hope the above information is helpful for you. If there's anything else I can help you with, please feel free to reach out again. 

    Thank you very much for your understanding and your cooperation.

    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.

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  1. Kristen-L 2,400 Reputation points Microsoft External Staff Moderator
    2025-08-20T21:34:38.7633333+00:00

    Hi @Jero Cheng,

    Hope things are running smoothly on your end.

    Following up on the support thread we've been working on. I hope the information I shared in my previous answer resolve the issue you were facing. If you are still facing the same issue or need assistance with anything else, kindly respond to this email, and I will be happy to help.

    We want to make sure everything is working as expected and that your experience remains uninterrupted.

    Thank you for your patience and understanding throughout the troubleshooting process. 

    I look forward to hearing from you soon.

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  2. Kristen-L 2,400 Reputation points Microsoft External Staff Moderator
    2025-08-21T22:27:01.6266667+00:00

    Hi @Jero Cheng,

    I hope you are having a great day.

    I'm reaching out again to follow up on your issue and check if everything has been resolved. My goal is to ensure your experience remains smooth and hassle-free. If you're still encountering any problems or have run into new challenges, please let me know which steps you're currently stuck on and happy to provide further help whenever you need it. 

    If you have any further questions, feel free to tag me in your reply so I can assist you directly.

    Looking forward to your update.

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  3. Kristen-L 2,400 Reputation points Microsoft External Staff Moderator
    2025-08-25T20:08:21.99+00:00

    Hi @Jero Cheng,

    Thank you for your detailed follow-up.

    You're trying to remove former employees from a mailbox delegate list in Exchange Online, but encountering errors because their accounts no longer exist in Azure AD or Exchange Online. This is a common issue when dealing with legacy or on-premises accounts that were never properly synced or cleaned up.

    When a user is deleted from Azure AD or Exchange Online, their delegate permissions may persist as orphaned entries - often represented by their SID (Security Identifier) rather than a valid user object. PowerShell commands like Remove-MailboxPermission or Remove-MailboxFolderPermission typically fail if the user object is missing or invalid.

    Here're solutions you can try:

    1. Use PowerShell to reset delegate permissions

    If the user object is gone, you can try resetting the delegate list entirely:

     

    Remove-MailboxFolderPermission -Identity ******@domain.com:\Calendar -ResetDelegateUserCollection

    This command clears all delegate permissions from the calendar folder.

    2. Remove permissions by SID (if visible)

    Run this to inspect current permissions:

    Get-MailboxFolderPermission -Identity ******@domain.com:\Calendar

    If you see entries with unresolved SIDs or strange aliases, you may need to remove them manually using:

     Remove-MailboxFolderPermission -Identity ******@domain.com:\Calendar -User "SID or alias"   

    3. Disable AutoMapping

    If the mailbox still appears in Outlook even after removing delegation, disable automapping:

    Remove-MailboxPermission -Identity "MailboxIdentity" -User "DelegateIdentity" -AccessRights FullAccessAdd-MailboxPermission -Identity "MailboxIdentity" -User "DelegateIdentity" -AccessRights FullAccess -AutoMapping $false

    This prevents the mailbox from auto-appearing in Outlook clients.

    4. Fallback: recreate and remove

    If the user was deleted recently (within 30 days), you can:

    • Restore the user temporarily.
    • Remove the delegation.
    • Delete the user again.

    Thank you for your cooperation and understanding. If there's anything else I can help you with, please feel free to reach out again.  

    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. 

     

  4. Kristen-L 2,400 Reputation points Microsoft External Staff Moderator
    2025-08-28T21:19:34.52+00:00

    Hi @Jero Cheng,

    Thank you for your detailed update.

    It’s fantastic to hear that the issue involving User G and User B has been successfully resolved! I truly appreciate you taking the time to follow the steps I provided and for sharing your experience with the outcome. 

    Regarding the new issue you're encountering where you're trying to remove delegate permissions for User C and User D from User B’s calendar using PowerShell, but they still appear in the output of Get-MailboxFolderPermission even though they no longer show in Outlook.

    The error message: "There is no existing permission entry found for user:'UserC'" means that User C does not have explicit folder-level permissions on User B's Calendar, so Remove-MailboxFolderPermission cannot remove what doesn’t exist.

    Here are some steps you can try to fix the issue:

    1. Verify Permissions again

    Run:

    Get-MailboxFolderPermission -Identity UserB:\Calendar | Format-List

    This will show detailed permission entries and help confirm if User C and User D are still listed with any permission roles.

    2. Try Force removal

    If they are still listed, try:

    Remove-MailboxFolderPermission -Identity UserB:\Calendar -User UserC -Confirm:$false

    This skips confirmation and may help if the issue is related to interactive prompts.

    3. Use Set-MailboxFolderPermission for Cleanup

    If removal fails, you can overwrite their permissions with:

    Set-MailboxFolderPermission -Identity UserB:\Calendar -User UserC -AccessRights None
Set-MailboxFolderPermission -Identity UserB:\Calendar -User UserD -AccessRights None

    This effectively nullifies their access.

    4. Check for hidden delegates

    Sometimes, delegates are stored in hidden mailbox settings. Use:

    Get-Mailbox -Identity UserB | Select-Object GrantSendOnBehalfTo

    If User C or User D are listed, remove them with:

    Set-Mailbox -Identity UserB -GrantSendOnBehalfTo @{remove="UserC","UserD"}

    Thank you for your patience and your understanding. If you have any questions, please feel free to reach out. 

    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.

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