Adding an Additional Mailbox to Outlook Crashed the App

How to Repair and Recover Outlook PST Files?

Microsoft Outlook is a robust business-class email client, popularly used to access Exchange Server and Office 365 accounts or mailboxes. It creates a local OST file where all the mail items, such as emails, contacts, notes, tasks, etc., are stored.

However, users sometimes encounter errors or issues in Outlook while accessing their mailbox. Outlook crashes while opening additional mailboxes is one of the issues you may encounter, especially if you have recently upgraded the Windows or Outlook client.

In this article, we have shared the solutions to fix the Outlook crashes when adding the additional mailbox.

Solutions to Fix Outlook Crashes when Adding or Opening Additional Mailboxes

Follow the solutions below to fix the Outlook crashes after adding or opening additional mailboxes.

Before you proceed to the solutions, ensure the following:

  • You have full access permission to the additional mailboxes you are adding.
  • You have valid credentials to access the additional mailboxes.

Remove the Additional Profile

If you have more than one Exchange profile or account in your Outlook, remove the one that doesn’t have the delegate or full access to the additional mailbox you want to add or open in Outlook. Follow these steps:

  • In Outlook, go to File > Info > Account Settings and click Account Settings.
  • You will see all the accounts added to Outlook. Choose the account you want to remove and click the Remove
  • Click Yes when you see the prompt for removing the account.
  • Close the Account Settings dialog box.

You can now add other users’ mailboxes as additional mailboxes in Outlook.

  • In Outlook, go to File > Info > Account Settings > Account Settings.
  • Choose the primary account and click Change.
  • Click More Settings.
  • Under the Advanced tab, click Add.
  • Type the mailbox name and click OK. Ensure the additional mailbox name is correct.
  • Once you make these changes, the additional mailboxes will be displayed in the Microsoft Exchange dialog box. Click OK.
  • In the Change Account dialog box, click Next > Finish > Close.

Note: In Outlook 2010 and later or Outlook for Office 365, use the manager’s mailbox profile to configure the delegate for the mailbox with default settings.

Disable Auto-Mapping for Shared Mailboxes

You may also disable auto-mapped user or shared mailboxes to fix the issue. As these mailboxes are auto-mapped and added automatically, disabling them can help you manually add and access the additional mailboxes.

To disable auto-mapping, you need administrator access to the Exchange Server. If you are not an administrator but a user, contact your IT department to help you resolve the issue. The detailed steps are here.

Remove Auto-Mapped Mailboxes

Although you can’t disable auto-mapping as a user, you can remove the auto-mapped mailboxes from the Outlook and then add them manually to access them without encountering errors.

To remove the mapped mailbox, follow these steps:

  • In Outlook, go to File > Info > Account Settings > Account Settings.
  • Choose the mailbox you want to remove and click Remove.
  • Confirm the mailbox removal by clicking Yes.
  • The mailbox will be removed.

You may now add the mailboxes manually.

Recreate OST File

Finally, when nothing works, you may try recreating or rebuilding the OST file by following these steps:

  • Open Control Panel, search and click on Mail.
  • Click Data Files and then select the profile.
  • Click Open File Location.
  • Copy the OST file that belongs to your profile to a different location as a backup. Make sure Outlook is closed before copying the OST file.
  • Once copied, you can delete the OST file from the location.
  • After deletion, open Outlook. This will recreate a new OST file.

If the problem has occurred due to an inconsistent OST file, this can help quickly resolve the problem and allow you to add additional mailboxes to your Outlook profile.

After the mailboxes are added, verify all mail items. If some mail items or folders are missing from the profile after recreating OST, you can use an OST to PST converter software to extract missing mail items from the backup OST file to PST format and then import the PST into your Outlook profile. This will restore all the mail items with complete integrity.


In Outlook, you can add and access multiple user mailboxes that you have full permission to access, including shared mailboxes. You may also use login credentials for a mailbox to add it to your existing Outlook profile. But sometimes, due to misconfiguration or multiple delegate profiles, Outlook cannot load the mailboxes and crashes. To resolve this problem, we have shared a few quick solutions you may apply to resolve the issue in your Outlook 2010 or later versions, including Outlook for 365. You may also check your OST file and recreate it. You can use an OST to PST converter tool to extract and restore the mail items from OST to a new Outlook profile with complete integrity and precision. By using the software, you can also export the mail items directly to your mailbox on live Exchange Server or Office 365.

Ganesh Kolekar is a graduate and geek. He is the man behind keeping the quality of the posts and manages the content part on the website.

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