OST to Office 365 migration
Importing data from an OST file to Office 365 becomes essential when access to the original Outlook profile linked to Exchange, IMAP, or any other mail server is no longer available. OST files can become orphaned, corrupt, or inaccessible, preventing access to emails, contacts, and calendar items. In such cases, the EdbMails OST to Office 365 Migration tool provides a reliable, direct solution by allowing you to securely upload OST data to Office 365 mailboxes without needing the original server or Outlook profile. It simplifies the entire process and ensures that folder structures and message properties remain intact.
By moving data to Office 365, you gain a secure, cloud-based environment with features like Exchange Online and seamless Microsoft 365 integration. This ensures continuous access to important information across devices, even if the original mail server is unavailable or the OST file is damaged. Migrating your OST data to Office 365 not only resolves immediate accessibility issues but also modernizes your email infrastructure with long-term flexibility, and enhanced collaboration.

EdbMails enhances the migration experience with secure OAuth 2.0 authentication, ensuring that your connection to Microsoft 365 remains protected throughout the transfer. As a trusted Microsoft partner, it delivers a fast and stable migration process designed for accuracy and reliability. Its incremental migration feature intelligently transfers only new or modified items after the initial upload, helping you save time, reduce bandwidth usage, and avoid duplicate entries.
With its built-in preview module, EdbMails allows you to verify mailbox contents from the OST file before starting the migration, ensuring complete clarity and precision. By combining enterprise-grade security, high performance, and an efficient workflow, EdbMails enables businesses to move OST data to Office 365 with maximum data integrity and minimal disruption.
Prerequisites to Import OST to Office 365
Before you import OST to Office 365, prepare the target Office 365 server as described in the following section.
- Ensure that you meet the network and bandwidth requirements for the migration. See network and migration planning, performance factors and best practices for Office 365 migration.
- Prepare your target Office 365 tenant. See tenant roadmap for Microsoft 365.
- Choose an Office 365 licensing plan that fits your requirements. You can also sign up for a 30-day free trial and decide on the most suitable plan later. To make an informed decision, compare the available Office 365 business plans as well as Office 365 enterprise plans to select the option that aligns with your organization’s needs.
- Create mailboxes for your users in your organization and assign suitable licenses to them.
Add users and assign licenses to Office 365 users
- If you plan to import Public folders from the OST file into Office 365, ensure that you create and configure the Public folder mailboxes on the target server.
- If you plan to migrate In-Place archives to Office 365, enable the archive mailbox on the target server. See steps to enable online archive in Office 365
- If you have a custom email domain from the source to which you want to receive emails after the migration, you must add and verify the custom domain on Office 365.
See steps to add a custom domain to Office 365 and steps to add DNS records to connect your domain
- Configure Office 365 to send and receive large messages
Follow the steps to increase the message size on Office 365 to 150MB.
Steps to Import OST to Office 365
Step 1: Download EdbMails OST to Office 365 Migration Tool
- Download and install the EdbMails application on your computer.
- See a detailed list of EdbMails system requirements for OST file conversion
- Launch the EdbMails application.
- Sign in using your email address and password, then click ‘Login’. If you’re new to EdbMails, simply select ‘Start Your Free Trial’ to continue with the trial version.Note: The Free Trial version allows you to explore all features and migrate up to 30 items from each and every folder. To migrate all the items, a license is required.
Click here to purchase the license from the EdbMails website.
Once your purchase is complete, close and reopen the EdbMails application, then log in again using the same email address and password used during license purchase. Your license will be activated automatically.
- Select ‘OST Recovery and Migration’
- Select ‘OST to Office 365’.
- You can continue with the default job name or select the ‘New Job’ button if you prefer to change the job name.
Step 2: Select the offline OST files
- Click ‘Browse for OST file'.
- Select the offline OST file 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 enabled.
Step 3: Preview and select the mailbox
- EdbMails thoroughly scans the offline OST file and restores mailbox data even in cases of damage or corruption. The software evaluates the internal structure of the OST and retrieves emails and other mailbox items. The duration of this process varies based on the file’s size and the extent of corruption. Allow the scan to finish completely to ensure accurate and comprehensive recovery of your data.
- Once the recovery process completes, EdbMails presents the restored OST mailbox in its full folder and subfolder structure within the main interface. You can easily navigate through any folder or subfolder to view its data. Selecting a specific category, such as Emails, Contacts, Notes, Tasks, or Calendar, displays all corresponding items, along with a detailed preview of the highlighted content on the right pane. EdbMails OST to PST Converter allows you to open an OST file without Outlook.
- Select the entire OST file or the required folders / subfolders and click the ‘Next’ button.
EdbMails flexible filtering options that help to customize your export process. For instance, you can apply date-based filters to export only the items that fall within a specific time range. To configure this, navigate to the ‘General’ section on the left pane and then open the ‘Settings’ tab located at the top-right corner.
Click here to learn more about setting date filters for OST to PST conversion.
Step 4: Connect to the target Office 365 server
- Click ‘Add New Connection’ to create a new connection to the target Office 365 server. To reuse an earlier configuration, select it from the connection list and click the ‘Connect to Existing’ button to continue.
- Select the required connection options and click the ‘Next’ button.
- Choose your preferred authentication method and then click ‘Login’ to proceed.
Connect to Office 365 server using secure modern authentication
- Authenticate on Microsoft sign-in page.
- Select one of the methods to load the mailboxes. You can also load the mailboxes using a CSV file.
Step 5: Map source and target mailboxes
- Choose the required mailbox mapping option
- EdbMails automatically creates mailboxes on your target Office 365 server and assigns the necessary licenses.
Learn more about the automatic mailbox creation process on the target Office 365 server.
- By default, EdbMails performs automatic mailbox and folder mapping between the source and target servers, ensuring a smooth and consistent migration experience. You can also manually map individual source mailboxes to their corresponding target mailboxes, enabling precise alignment based on your organizational or user-specific requirements.
Step 6: Start OST to Office 365 migration
- Click the 'Start Migration’ button to initiate the migration process.
- The migration process is in progress, and you can monitor it in the progress bar. You also have the option to pause or resume the operation at any time. Once the migration operation is completed, EdbMails will display a confirmation message.
- You can verify the list of migrated folders and mailbox items with EdbMails text-based migration log report.
- Login to your target Office 365 server and verify the migrated items.
OST to Office 365 Post-Migration Tasks
- Step 1: Update the MX records to point to Office 365
Update the MX records to direct incoming emails to the target Office 365 server, ensuring email delivery. Additionally, set up the Autodiscover record to enable Outlook to automatically connect to the newly migrated mailboxes.
- Step 2: Create a new Outlook profile for users in the new domain
Configure the Outlook profile for each user in your domain if Outlook has problems connecting to Office 365 mailboxes.
- Step 1: Update the MX records to point to Office 365
Troubleshooting Guide for OST to Office 365 Migration
For troubleshooting, visit our Knowledge Base. For more queries, refer to the Frequently Asked Questions or reach out to our support team.
Benefits of EdbMails to Import OST to Office 365
- Recovery and Direct Migration: EdbMails helps you recover mailbox data from corrupted or "orphaned OST files". Once the data is restored, the software enables you to directly import OST to Office 365 and migrate data to the Live Exchange server without requiring multiple tools or manual steps, making the entire process smooth and reliable.
- Rebuilding and Conversion: With EdbMails, you can rebuild Outlook data files and convert OST to PST using the same application. This streamlines mailbox management by eliminating the need for multiple tools, while the integrated interface ensures a seamless repair and conversion process.
- No Size Limit: EdbMails enables importing mailboxes from OST to Office 365 without imposing size restrictions. This ensures smooth migration for large mailboxes, archive folders, or large OST files without slowing down the migration process.
- Broad Compatibility: EdbMails works seamlessly on all Windows operating systems and supports OST files from a wide range of Outlook versions, including 2021, 2019, 2016, 2013, 2010, 2007, and 2003. This wide compatibility makes it suitable for both modern environments and legacy systems.
- Secure Authentication: EdbMails ensures a high level of security when you import OST to Office 365 by not storing your login credentials and using secure OAuth 2.0 modern authentication along with TLS encryption throughout the migration process. This security framework keeps your Office 365 connection safe and protected throughout the migration process.
- Recovery of Deleted Items: EdbMails can retrieve and migrate deleted email items from OST to Office 365. This allows users to restore accidentally removed messages and ensure complete mailbox continuity when moving to Office 365.

