Shared Mailbox Errors

Question

Shared Mailbox Errors

MDean 0

What are some options I can take to troubleshoot or resolve shared mailbox errors?

Our IT department has had us clear the cache, switch back and forth between the desktop and web version; yet we continue to experience issues. When trying to update meeting invites, the action will fail and a message will display that the action can't be performed, try again later. We receive many NDR emails bouncing back. Sometimes trying to send an email just spins and spins on the desktop version, switch to web based and try to perform the same action....it just spins and spins.

We have used both classic and new outlook versions to try and push through what we need to send out.

0 comments

2 answers

Your answer

Answer 1

Kudos-Ng 15,050 Microsoft External Staff Moderator

Hi MDean,

Thank you for posting your question in the Microsoft Q&A forum.

Based on your description, it appears the problem is directly related to the shared mailbox, as you've confirmed it occurs across all Outlook versions (Classic, New Outlook, and OWA). To better understand and troubleshoot this issue, I'd like to gather some additional information:

Did these operations (updating meeting invites, sending emails) work normally before, and the issue started recently? Or is this the first time setting up this shared mailbox and encountering these errors?
Does this issue affect multiple users accessing the shared mailbox, or is it isolated to specific users?
Is this problem occurring with one specific shared mailbox, or across all shared mailboxes in your environment?

While waiting for more details, here are some steps you can try based on my initial assessment:

Since you're receiving NDR bounces, it's possible that the shared mailbox is being blocked from sending messages to meeting attendees. The most common cause is missing "Send As" permission. Ensure that users who need to update meetings or send emails from the shared mailbox have "Send As" permission explicitly granted (not just "Full Access").
Verify if there are any recently created transport rules or delivery restrictions that might be blocking emails sent from the shared mailbox.

I also found a Microsoft article about a known issue related to updating meetings in shared calendars, though the symptoms aren't identical to yours. It may be a contributing factor:
Users may experience an error when updating a meeting in their own or a shared calendar

Looking forward to your update.

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.

Kudos-Ng 15,050 Reputation points Microsoft External Staff Moderator

2026-02-13T14:27:45.3733333+00:00

Hi MDean,

Just checking in to see if you had a chance to review the previous response.

Your feedback would be very helpful in ensuring everything is on track.
MDean 0 Reputation points

2026-02-13T14:43:42.8133333+00:00

Hi, we continue to encounter issues and it's mainly tied a daily limit that we are exceeding. The work arounds that were provided to us by IT were not feasible for our needs and therefore a second email account was required to be created to try to navigate through the Microsoft constraints that we were told are hard coded into the settings.
Kudos-Ng 15,050 Reputation points Microsoft External Staff Moderator

2026-02-23T12:48:17.8066667+00:00
Hi MDean,

Thank you for following up and for sharing the additional context.

It looks like you’ve already investigated the issue related to the daily limit for sending invitation emails. I did some further research and found that Microsoft has documented a scenario that aligns with what you're experiencing. Here are some key insights:

In Exchange Online, the maximum number of recipients for any outgoing meeting message, whether a new invitation, update, or cancellation is 5,000 recipients.

However, an important behavior to note is that when attendees respond to a meeting invitation (accept, tentative, or decline), Outlook adds each respondent individually to the tracking list. Over time, this list can grow significantly, potentially preventing the organizer from sending future updates or cancellations.

Microsoft has documented this scenario here: Scheduling meetings with hundreds of attendees.

To mitigate the issue, you can consider:

Using Distribution Lists to invite attendees, since a DL counts as only one recipient regardless of its member count.

Turning off meeting response tracking if you don’t need to monitor who accepted or declined. This prevents Outlook from expanding the recipient list over time.

I hope this helps.
Kudos-Ng 15,050 Reputation points Microsoft External Staff Moderator

2026-02-24T14:01:24.8+00:00

Hi MDean,

Just checking in to see if you had a chance to review the previous response.

Your feedback would be very helpful in ensuring everything is on track.

Answer 2

To troubleshoot and resolve shared mailbox errors in Outlook, consider the following options:

Check Permissions: Ensure that you have the correct permissions to access and send emails from the shared mailbox. You may need to have both Full Access and Send As permissions. If you encounter errors related to sending emails, verify that these permissions are granted.
Replication Latency: If you recently created the shared mailbox or added users, there may be a replication latency issue. Wait for about an hour and try again, as the information may take time to propagate across all data centers.
Remove Automapped Mailboxes: If the shared mailbox is automapped in Outlook and causing performance issues, consider removing it. You can do this by checking your account settings and removing the shared mailbox from the list of additional mailboxes.
Limit Open Shared Mailboxes: Having too many shared mailboxes open can slow down performance. Try to reduce the number of shared mailboxes you have open in Outlook.
Use Outlook in Online Mode: If you are experiencing issues in Cached mode, switch to Online mode to see if that resolves the problem. Sometimes, Cached mode can lead to errors when sending emails.
Clear Cache Again: If clearing the cache previously didn’t resolve the issue, try doing it again or consider resetting your Outlook profile.
Check for Updates: Ensure that your Outlook application is up to date. Sometimes, updates can fix bugs that may be causing issues with shared mailboxes.
Run Microsoft Support and Recovery Assistant: This tool can help diagnose and fix issues with Outlook and shared mailboxes.

By following these steps, you may be able to resolve the issues you are experiencing with shared mailboxes in Outlook.

References:

Share via

Shared Mailbox Errors

2 answers

Your answer