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The Powerful Guide To Shared Mailbox Performance Issues (2023)

The strategies in this post will help you solve shared mailbox performance issues.

When you start Microsoft Outlook, switch folders, or synchronize email, you may experience slow performance. You have many shared folders, mailboxes, or both, open in Outlook. In the case of a shared calendar, modifications or additions cannot be made until the program is finished syncing updates.

The number of shared folders and mailboxes that you can have open without issues depends on several factors, including hardware, mailbox size, size of the shared folders or mailboxes, number of folders in a shared mailbox, item count in folders, and network speed. A computer that has slower hardware, a large mailbox, and a slow network connection may not be able to open more than five shared folders or mailboxes. However, a faster computer that has a smaller mailbox and a fast network connection may be able to open 10 or more shared folders or mailboxes.


Reduce the number of shared folders or mailboxes that you have open in Outlook. To do this, you must first determine whether you have shared folders or shared mailboxes open. If you have shared mailboxes open, you must also determine how they are opened, such as whether they are opened manually as an additional mailbox or whether they are opened because of AutoMapping.

  • A shared mailbox appears below your own mailbox in the Folder Pane, as shown in the following screenshot.
shared mailbox performance issues
  • A shared folder appears below Shared <Folder type>, such as Shared Calendar or Shared Contacts, as shown in the following screenshot.

Remove a shared mailbox

If you have a shared mailbox open in Outlook, it was either manually added under Open these additional mailboxes or it was opened automatically because of automapping. You can determine how the shared mailbox was opened and remove the shared mailbox by following the steps in the following sections.

Remove a shared mailbox that was opened as an additional mailbox manually

  • Select FileAccount Settings, and then Account Settings.
  • Select the Microsoft Exchange account, and then select Change.
  • Select More Settings.
  • On the Advanced tab, you can view any manually added shared mailboxes below. Open these additional mailboxes.
  • Select the shared mailbox, and then select Remove.
  • Select Yes to confirm that you want to remove the mailbox, and then select OK.
  • Select Next, and then select Finish.
  • Select Close on the Account Settings window.

If the shared mailbox does not appear below Open these additional mailboxes, try the below option.

  • Select File > Account Settings > Account Settings.
  • On the Email tab, select the Shared mailbox account, then click Remove.

This will not impact any of the data in the shared mailbox. By choosing Remove you will simply be removing access to Outlook.

Note: If the shared mailbox does not appear in these options, it is likely automapped. You have to work with your administrator to remove the automapped mailbox from Outlook.

To remove an automapped mailbox from Outlook, use one of the following options:

  • Remove your full access permissions from the mailbox. This is a good option if you no longer need access to the shared mailbox.
  • Remove automapping for the shared mailbox. This is a good option if you must have access to the shared mailbox but do not want it automapped in Outlook.

Also read:

Remove shared Calendar, Contacts, Tasks, or Notes folders

  • Open Outlook.
  • Select the Calendar, Contacts, Tasks or Notes folder in the Navigation pane in which you have a shared folder open.
  • Look under Shared <Folder name> for any shared folders, as shown in the following screenshot.
  • Right-click the shared folder, and then select Delete Folder or Delete Calendar, depending on the folder type. The following screenshot shows a shared calendar being removed.

Note: Selecting Delete Calendar or Delete Folder on a shared calendar or shared folder does not delete the folder from the mailbox where it resides. This action removes the folder from your Outlook view delete folder only.

  • Follow these steps for any remaining shared folders that you want to remove from Outlook.

Close a Shared Inbox Folder

When you open a shared Inbox folder, it appears in Outlook only until you select a different folder. It does not remain in the folder list. To remove a shared Inbox folder, close it by selecting a different folder in your mailbox.

Online archive

If you have enabled the online archive mailbox, archive items to the online archive mailbox.

Retention Policy – Calendar

Apply a retention policy to the Calendar folder to delete items from this folder. (For example, any item that is not modified within one year moves to the Deleted Items folder.)

Best Practices

When there are too many designated users concurrently accessing a shared mailbox (no more than 25 is recommended), they may intermittently fail to connect to this mailbox or have inconsistencies. In this case, you can consider reducing the number of users or using a different workload, such as a Microsoft 365 group or a public folder.

That’s how you can solve the shared mailbox performance issues.

Now I want to turn it over to you.

Which strategy from today’s guide are you going to try first? Or maybe you have a question about something that I covered.

Either way, I’d like to hear from you. So go ahead and leave a comment below.

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