Migrating from PST files to Office 365 involves transferring email data stored in Outlook PST files to the cloud-based Office 365 environment. This process can be complex and requires careful planning and execution to ensure a smooth transition. Using R[b]egain PST to Office 365 Migration Tool.
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Here's a general outline of the steps involved:

Assessment and Planning:

Evaluate your current email infrastructure, including the number of PST files, their size, and the content they hold.
Determine the migration method that best suits your organization's needs, such as using third-party migration tools, PowerShell scripts, or manual methods.

Plan the migration timeline, considering potential downtime and user impact.

Choose a Migration Method:

Network Upload: Upload PST files over the network to the Azure Storage service, and then import them into Office 365.
Drive Shipping: Ship physical hard drives containing PST files to Microsoft, who will then upload the data to Office 365.
Third-Party Tools: Use specialized migration tools that offer advanced features and options for a smoother migration process.

Prepare Office 365:

Set up user accounts and licenses in Office 365 for the users whose data will be migrated.
Assign necessary permissions and roles to administrators and users involved in the migration.

To know more detail visit this post - PST to Office 365 Migration Tool