To resolve errors while import PST files into Microsoft 365, start by verifying the PST file's integrity. Corrupt or oversized PSTs often cause import failures, so use a reliable PST repair tool like Aryson Outlook PST Repair to fix corruption, recover lost emails, and handle encrypted or password-protected files. Ensure the PST format is compatible--convert ANSI PSTs to Unicode if needed. Check permissions and roles in Microsoft 365; proper admin access is essential for importing mailbox data. Avoid network interruptions during uploads and make sure the Outlook version and mailbox size comply with Microsoft 365 limits. If selective data is needed, use filters such as date range to prevent timeouts. Finally, always backup PST files before import to prevent data loss, and consider importing in smaller batches for smoother processing.