Migrate Large Number of Outlook Data Files (PST) to Office 365 Without Downtime?

Whether you are an admin, an MSP for a business unit, or an individual – migrating user mailbox data in PST to Office 365 is a complicated task. It may seem simple to use manual methods like network upload or drive shipping, or even syncing Outlook with Office 365. But it is quite risky.

Improper planning while migrating Mailbox data to tenant accounts in the cloud email client can cause problems, such as:

• Unnecessary downtime
• Missing emails, contacts, calendars or other items from the mailbox
• Insufficient allocated space in the Azure cloud storage
• Users facing login issues

Let’s read further and learn how to plan for a smooth and compliant PST to Office 365 migration process.

What are the Challenges Faced while Migrating PST Files to Office 365 in Bulk?

It is quite a challenging task to import PST files to Office 365 on a large scale. Here are some challenges that you may encounter:

• Transferring or moving PST files in bulk without impacting business operations
• Uploading large amount of mailbox data (in GBs) in PST files without overwhelming the existing network infrastructure
• Missing or skipped items after migration due to corruption or mapping errors

How to Prepare for Large-Scale PST to Office 365 Migration?

Here is how to plan for a large-scale Outlook data migration to Office 365:

Step 1: Conduct pre-migration Assessment

Here, you’ll need to carefully analyze the user mailboxes and identify the data listed below for each PST file.

• Owner
• Size
• Name of the file
• Source
• Size of disconnected PST files

Gathering this information will help you correctly map the target accounts with the source files. With this, you’ll have the total volume of the data to be migrated. Also, it will help identify any possible issues beforehand that you can fix before starting the import job.

Step 2: Define Data Migration Needs

You’ll have to define certain needs of the mailbox migration process. Eg. you may need to:

• Ensure data integrity of all the directories and files during the migration process
• Maintain data security throughout the process using an encrypted transfer method or secure access controls
• Optimize the performance of the PST migration process so that it handles large volumes of datasets efficiently, with minimal downtimes or network disruptions

Step 3: Select a Migration Strategy

Microsoft has defined various migration strategies that you can deploy based on your business goals. There are several key indicators that can aid you in choosing the right migration strategy.

Step 4: Choosing the Right PST to Office 365 Migration Method

After you have identified your PST files, defined data migration needs, and selected a suitable migration strategy for your PST files, you’ll need to choose the most apt method to migrate PST files to Office 365. Now, there are two manual ways to do it.

1. Network Upload – This is a free method by Microsoft where you can directly upload PST files to Office 365. For this, you’ll need to first sign in to Exchange Admin Center to assign Mailbox Import Export roles. Then, you’ll create a PST import job in Microsoft Purview (accessed via EAC). Next, run a PowerShell command to use the SAS URL and AzCopy tool to upload the PST files to a temporary Azure Storage space. Once the files are in the cloud storage, you will run the import job, wherein it will use a mapped CSV file to migrate the uploaded PST files to the target mailboxes in Microsoft 365.
2. Drive Shipping – This is another free way to migrate PST files to Office 365. Here, you’ll need to download the PST import tool to select the external HDD. Then, copy all the PST files that you want to transfer to the cloud environment to a BitLocker-encrypted external HDD. After this, you’ll have to create a PST import mapping file (CSV file) and validate it in the next step – create an import job via Microsoft Purview. Then ship the drive to a Microsoft data center, where a professional will upload your files to the Azure Storage space. Here, you will have to pay Microsoft to upload your data. You will also have to bear the shipping charges.

Limitations of the manual methods

The above-mentioned manual methods have the following limitations:

• Lengthy and time-consuming
• Not suitable for large-scale PST file migration, as a large number of files will slow down the process
• Additional resources are required in case of Drive Shipping
• Not suitable for PST files larger than 20 GB
• The PST ingestion rate in Microsoft 365 is 24GB/day. This makes the process very slow if there are 100s of GBs of PST files to migrate to O365.

Step 5: Post Migration Steps

Large-scale PST file migration takes time to complete. After the process is over – depending upon the volume of data – you’ll need to follow some steps to validate the data. Here’s a list of items you will have to check:

• Folder structure
• Email count
• Attachments
• Calendar items
• Contacts
• Linked PST files

It can be quite a laborious task to validate a large number of accounts and the associated mailbox data on your own. Hence, you may ask users to verify the above list of items themselves. This will help you expedite this step and close the process in due time.

What is the Best Way to Migrate PST Files to Office 365?

As mentioned above, traditionally migrating PST files to Office 365 at a large scale is not efficient. They are lengthy, complicated, and time-consuming. Moreover, you may need to use additional resources (in the case of Drive Shipping). Hence, if you are looking to move 100s of GBs of mailbox data to Office 365, then these aren’t suitable.

To make it simple, you can deploy a specialized PST to Office 365 migration tool. Stellar Migrator for Outlook is one such powerful tool that simplifies the PST to O365 migration process. It is a user-friendly tool that can easily be installed on any system and used without any difficulties to migrate PST files to Microsoft 365 accounts. You can directly migrate Outlook data to the tenant accounts in Office 365 without installing the Outlook client on your system.

Salient features of Stellar Migrator for Outlook:

• Conveniently migrate PST files to Office 365
• Preserves mailbox folder structure and hierarchy during the migration
• Pay-per-use licensing makes it a cost-effective solution for large migration tasks
• Migrates PST files to Office 365 in the following scenarios:
  • Directly import PST to O365
  • Migrate PSTs from any system/s or network path
  • Migrate encrypted OST and PST files
• Automatic target mailbox mapping
• Supports incremental migration, which minimizes data duplicity
• Shows real-time progress of the process

Conclusion

For businesses, performing a large-scale PST migration job is not just another task. It is a strategic undertaking to modernize existing infrastructure. Such a move ensures that critical data is secured from malicious attacks, and business operations don’t disrupt even during server downtimes.

Microsoft’s suggested methods – Network Upload and Drive Shipping – are slow, resource-intensive, and lengthy. Hence, they are inefficient while migrating PST files in bulk. Instead, you can take a safer and faster approach – an advanced tool like Stellar Migrator for Outlook. It is a powerful tool that safely migrates PST files to Office 365, without any hassle.