How to Transfer a Large Mailbox from Office 365 Outlook to Webmail: A Step-by-Step Guide

Transferring a large mailbox from Office 365 Outlook to Webmail may seem daunting, but with the right tools and a clear process, it can be done efficiently. I recently completed such a task, and I’m here to share the steps I followed. Here’s a breakdown of the process to help you successfully transfer your emails.

Step 1: Generate .PST Files Using the eDiscovery Tool from Microsoft Compliance

The first step involves exporting the mailbox data as .PST files using the eDiscovery tool available in Microsoft Compliance. Here’s how you can do it:

1. Log in to the Microsoft 365 Compliance Center.
2. Navigate to Content Search under the eDiscovery section.
3. Create a new search query and specify the mailbox you want to export.
4. Run the search and wait for it to complete. Once done, click on Export Results.
5. Generate an export key and download the eDiscovery export tool. Use the key to export the mailbox data as .PST files.

This step ensures you have all the mailbox data securely exported for the next steps.

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Step 2: Download All .PST Files to the Local Computer

After generating the .PST files, download them to your local computer. This step ensures you have physical access to the data, making it easier to work with during the transfer process.

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Step 3: Export Data in Outlook Desktop and Merge All Files into a Single .PST File

To simplify the data transfer, merging all .PST files into a single file is ideal. Here’s how you can do it:

1. Open Outlook Desktop on your computer.
2. Go to File > Open & Export > Open Outlook Data File and import each .PST file one by one.
3. Once all .PST files are loaded, create a new data file by navigating to File > Account Settings > Data Files > Add.
4. Drag and drop all emails and folders from the imported .PST files into the new single data file.

This consolidated file will streamline the next step of transferring the emails to the desired account.

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Step 4: Sign in to the Desired Email Address in Outlook 365 Desktop

Next, set up the target email account where the mailbox data will be transferred. Follow these steps:

1. Open Outlook Desktop and navigate to File > Add Account.
2. Enter the email address and credentials for the desired Webmail account.
3. Once configured, ensure the mailbox is synced and ready to receive data.

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Step 5: Move All Emails from Outlook Export .PST Folder to the Target Email

With the target email account configured, the final step is moving the emails:

1. In Outlook, open the single .PST file you created earlier.
2. Select all the emails, folders, and subfolders within the .PST file.
3. Drag and drop them into the desired mailbox in the Outlook folder pane.

Depending on the size of the mailbox, this process might take some time. Ensure the transfer completes without interruptions.

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Conclusion

Transferring a large mailbox from Office 365 to Webmail is a multi-step process that requires attention to detail. By leveraging tools like Microsoft Compliance’s eDiscovery and Outlook Desktop, you can ensure a smooth migration. Following the steps outlined above, I successfully moved all emails without losing any data. Whether you’re managing a personal migration or handling this for a client, these steps should help you navigate the process seamlessly.

Tags: Microsoft 365outlook 365Tech support