The most useful method is to use a dedicated PST splitter tool that can split by size, year, or folder while preserving data integrity and Outlook hierarchy. Such tools let you choose criteria (e.g., 1–5 GB chunks, year-based archives like 2018/2019/2020, or per-folder splits such as Inbox/Sent/Archive), handle very large Unicode PSTs, and avoid corruption risks tied to manual export/import workflows.​

Why a dedicated splitter

• Purpose-built utilities preserve metadata, folder structure, and attachments while dividing oversized PSTs, minimizing corruption risk and reindex time.​
• They support common split modes—by size, date/year, folder, sender/email ID—and often work without Outlook installed, speeding up operations on big archives.​​
• Many handle ANSI and Unicode PSTs, password-protected files, and generate reports for auditability—useful for IT admins and power users.​​

Best-practice approach

• Choose split-by-size when Outlook performance degrades or storage quotas require smaller files; 2–5 GB segments are a practical baseline for manageability.​
• Choose split-by-year to create clean annual archives that align with retention and e-discovery timelines (e.g., one PST per year).​​
• Choose split-by-folder if you want operational separation (e.g., separate PSTs for Inbox, Sent Items, or project folders) to streamline search and backup.​

Notable options to consider

• vMail PST Splitter: splits by size, date, folder, email ID, subject, sender, or year; supports ANSI/Unicode; works without Outlook; keeps hierarchy; outputs a summary report.​
• SysCurve PST Splitter: supports split by size, folder, and year; maintains data integrity and common criteria like date/email ID.​
• Kernel/Nucleus PST Splitter: supports ANSI/Unicode, date-range presets, folder-specific extraction, and password-protected PSTs.​

Practical tips

• Validate PST health before splitting; even good tools may skip corrupted items if the source PST is already damaged.​
• Plan naming conventions (e.g., Acme_Jan2018–Dec2018_Archive.pst) and target locations for simpler indexing and backup.​
• After splitting, add PSTs one at a time in Outlook to reduce initial reindex load and confirm hierarchy and counts match the tool reports.​​

In short, the most reliable, time-efficient method is to run a PST splitter tool and choose the split mode that matches your goal: size for performance, year for compliance-friendly archives, or folder for workload separation.​​

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