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Backup Exchange Mailbox using OST File

Exchange Online does not include a built-in option for traditional mailbox backups, so restoring a mailbox to a previous state is not possible. To support offline access, Outlook uses Cached Exchange Mode, which creates a local OST (Offline Storage Table) file that holds a synchronized copy of mailbox data.

These OST files contain a replica of mailbox content from Exchange Server, Office 365, or IMAP accounts, allowing users to work even without an internet connection. However, because an OST file is linked to a specific Outlook profile, it cannot be used independently as a backup or imported directly if the original mailbox is removed or becomes unavailable.

Exchange mailbox backup using OST

To ensure mailbox data is preserved and accessible independently of Outlook or the original account, converting the OST file to PST format provides a dependable solution. EdbMails OST to PST Converter simplifies this task by extracting data from OST files - whether active, orphaned, or corrupted and exporting it to PST format, which can be easily opened in Outlook.

This step-by-step guide explains how to backup Exchange mailboxes using OST files, covering both manual procedures and automated methods with EdbMails.

Reasons for mailbox backup and conversion of OST file to PST

Exchange Server Downtime or Failure: An Exchange server can crash or may go offline causing the local OST file to become orphaned, making mailbox data inaccessible through Outlook. In such scenarios, users may lose access to critical emails and folders. EdbMails can recover orphaned OST files and convert them into PST format without requiring the Exchange server, ensuring uninterrupted access to mailbox data.
OST Orphaning Errors: OST files are also orphaned due to Exchange server failures or EDB file corruptions can break the connection between the mailbox and its OST file, rendering the OST unusable within Outlook. EdbMails extracts data directly from OST files, even when the source Exchange database is damaged or unavailable, making it a reliable recovery solution.
OST File Corruption: OST files stored locally are vulnerable to corruption caused by virus infection, unexpected system shut-downs, Outlook crashes, hardware failures, or ransomware incidents. EdbMails uses advanced scanning algorithms to safely recover data from corrupt and virus-affected OST files and export it to secure PST files.
Manual OST Recovery: Manually repairing corrupted OST files is often complex, time-consuming, and rarely guarantees complete data recovery using native tools. EdbMails automates the recovery process and ensures complete mailbox extraction without relying on manual or error-prone repair methods.
Outdated OST Mailbox Data: Cached OST files may not always reflect the most recent mailbox updates from the server, especially after sync failures, making it difficult to retrieve recently lost data. EdbMails allows users to extract all available data from the OST file and securely store it in PST format for verification, backup, or further migration.
Oversized OST Files Issues: Overgrown OST files are difficult to manage and often cause synchronization errors, performance slowdowns, and Outlook instability. EdbMails supports splitting large OST exports into smaller PST files, improving manageability and preventing sync-related issues.
Accidental Mailbox Data Deletion: Accidental deletion of emails, folders, or entire mailboxes on the Exchange server can result in permanent data loss if backups are unavailable. EdbMails can recover deleted mailbox items from OST files and convert them to PST, providing an effective fallback when server-side recovery is not possible.

How to convert the OST file to PST?
Steps to backup OST to PST
Step 1: Download and install EdbMails OST to PST converter tool
- Download and install the EdbMails application on any Windows-based computer.
- Launch the EdbMails application.
- Enter your email address and password, then click ‘Login’. If you’re new to EdbMails, select ‘Start Your Free Trial’ to continue with the trial version.
  Note: The Free Trial allows you to explore all software features and export up to 30 items from each folder. To unlock full functionality, you must purchase a valid license from the EdbMails website.
  Click here to purchase a license from the EdbMails website.
  After completing the purchase, close and reopen the EdbMails application. Then sign in using the same email address and password used during purchase to activate your license.
- Select ‘OST Recovery and Migration’.
- Select ‘OST to PST’.
- You can retain the default job name or click the ‘New Job’ button to change the job name.
- Then click ‘Next’ to continue.
Step 2: Select the offline OST file
- Click ‘Browse for OST file'.
- Select the OST file that you want to export from your local drive, then click the ‘Next’ button to continue. You can also share the OST file on a network with read and write permissions assigned.
- Click ‘Browse’.
- Choose the location to save the exported PST files and ensure there is sufficient free disk space for storage.
- EdbMails thoroughly examines the offline OST file to retrieve mailbox data, even if the file is damaged or corrupted. It carefully evaluates the file structure and internal data to recover emails and other mailbox items. The scan duration varies based on the OST file size and the extent of corruption, so allow the process to finish to ensure complete data recovery.
- After the recovery process is completed, the OST file data is displayed in the application interface with its full folder and subfolder hierarchy. You can expand any folder or subfolder to view its contents. When you select a folder, such as Emails, Contacts, Notes, Tasks, or Calendar, the application lists all the items within it and displays a detailed preview of the selected content on the right side of the interface. EdbMails OST to PST Converter allows you to open an OST file without Outlook.
Step 3: Preview and select the mailbox
- Select the required mailboxes/folders and click the ‘Next’ button.
Step 4: Export the rebuilt OST file to PST
- EdbMails OST to PST converter ensures fast and accurate conversion of offline OST files to PST format. Review the selected mailboxes and folders for the export operation, ensure the ‘Action’ is set to ‘Export’, and then click the ‘Start Export’ button to begin the export process.
- The export operation is now initiated, and you can monitor it in the progress bar. Once the process is complete, EdbMails will display the export operation completion message.
- Backup all of your emails from the OST to PST.

Frequently Asked Questions (FAQ)

What is the difference between an OST and a PST file, and why convert OST to PST for mailbox backup?
An OST file (Offline Storage Table) is a synchronized local copy of an Exchange mailbox used by Outlook for offline access but cannot be imported directly if the server mailbox is unavailable. A PST file (Personal Storage Table), on the other hand, is a standalone Outlook data file that can be opened and managed independently. Converting OST to PST enables you to create a reliable backup of your mailbox data that’s portable and accessible even without the original Exchange profile.
Can I convert an offline or orphaned OST file to PST even if the Exchange server or Outlook profile is unavailable?
Yes, EdbMails does not require an active Exchange profile or server connection to convert an OST file. Even if your OST file is orphaned (i.e., disconnected from the server) or Outlook is no longer set up, EdbMails can still recover and export the mailbox data to a PST file.
Will converting an OST file to PST preserve all mailbox items and structure?
Absolutely. EdbMails maintains complete data integrity during conversion, retaining emails, contacts, calendars, attachments, folder hierarchy, and metadata. This means your backed-up PST reflects the original mailbox layout and content without loss.
Is an OST file suitable for long-term Backup Exchange Mailbox and data retention?
No, an OST file is only a locally synchronized copy tied to a specific Outlook profile and Exchange mailbox. To make Exchange mailbox data usable as a long-term backup, the OST must be converted into a portable format like PST, which can be opened independently in Outlook.
Is it possible to backup Exchange mailboxes from Exchange Online or Office 365 using an OST file?
Yes. OST files generated from Exchange Online (Microsoft 365) mailboxes can be converted into PST format using EdbMails. This provides an offline backup option for cloud mailboxes where traditional backup and point-in-time restore options are limited.