Slow Microsoft 365 shared mailbox when you make a folder

Question

It may take hours before others can see the folder.

Is there anything I can configure to make it faster?

If I install Exchange on-prem and synchronize with Exchange Online, will users experience faster speeds?

Best Regards

[Moderator note: personal info removed]

Answer 1

Hi Johnny Broe,

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

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Based on my research, folder synchronization in shared mailboxes typically takes a few minutes under normal conditions. However, if you're experiencing delays of several hours, there are a few settings and configurations you can check to improve this:

1) Disable Cached Mode for Shared Folders

If you have "Download shared folders" enabled in Outlook, this can cause significant synchronization delays, especially for large or busy shared mailboxes:

• Go to File > Account Settings > Account Settings
• Select your Exchange account and click Change
• Click More Settings, then the Advanced tab
• Uncheck "Download shared folders"
• Restart Outlook

This forces Outlook to access the shared mailbox directly from the server, which often results in faster synchronization.

2) Add the Shared Mailbox as an Additional Account

Consider configuring the shared mailbox as a separate account in your Outlook profile. This approach provides better performance and more granular control over caching settings. Follow the instructions in this official Microsoft article: Add a shared mailbox as an additional account

This method also unlocks features like rules, Out of Office settings, and calendar reminders that aren't available with standard auto-mapping.

3) Manual Synchronization

You can force Outlook to sync manually:

• Click on the shared mailbox in your folder list
• Press F9 to trigger Send/Receive for all folders

Regarding Your Question About Exchange On-Premises:

Installing Exchange on-premises and synchronizing with Exchange Online may introduce additional latency due to the extra hop through your on-premises infrastructure. The synchronization delays you're experiencing likely relate to how Outlook caches and syncs shared mailbox data, not the Exchange Online infrastructure itself.

I hope this helps. If you have any further questions, please feel free to share.

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Answer 2

To improve the speed of creating and synchronizing folders in a Microsoft 365 shared mailbox, consider the following options:

1. Reduce the Number of Shared Folders: If you have many shared folders open, it can slow down performance. Reducing the number of open shared folders or mailboxes may help improve synchronization speed.
2. Disable Caching of Shared Folders: Disabling the caching of shared folders can sometimes improve performance, especially in environments with many shared mailboxes. However, this means that shared folders will not be available offline.
3. Optimize Mailbox Sizes: Keeping mailbox sizes smaller can enhance performance. This is particularly important if you're working in an Office 365 environment.
4. Consider Network Conditions: Ensure that your network connection is stable and fast, as slow network speeds can significantly impact performance.

Regarding your question about installing Exchange on-premises and synchronizing with Exchange Online, this could potentially improve performance, especially if your on-premises infrastructure is optimized for speed and you have a fast local network. However, the actual performance gains would depend on various factors, including your specific setup and network conditions.

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References:

• Outlook performance issues when you have many shared folders or mailboxes open
• Performance and synchronization problems when you work with folders in a secondary mailbox in Outlook