PST/OST size limits across all Outlook versions and how to raise them.

• Outlook 2003 and 2007: ANSI .pst max size 2 GB. Unicode .pst max size 20 GB.
• Outlook 2010 and later (2013, 2016, 2019, 365): Unicode by default, max size 50 GB.
• Registry changes: Users can change Windows registry entries to raise or lower the limits. However very large .pst files can cause performance problems.

Important notes:

• .pst size limits depend on file format (ANSI or Unicode) and Outlook version.
• Very large .pst files can hurt Outlook performance and increase corruption risk.
• Microsoft recommends using mail servers instead of huge .pst files.