How to convert OST to PST file With the Help to Thrid Party Tool

Direct conversion of an .ost file to a .pst file using Outlook alone is not documented in the provided material, and the context does not describe or endorse any specific third‑party tools for this purpose.

However, the context does provide supported ways to work with Outlook data files:

1. Outlook Data Files (.pst) are used to store or archive mail, contacts, and calendar items locally. They are typically stored in Documents\Outlook Files and can be used to archive older items or export data when the online mailbox is nearly full.
2. Offline Outlook Data Files (.ost) are synchronized copies of server mailboxes (IMAP, Exchange, Outlook.com) stored under *drive*:\\Users\\user\\AppData\\Local\\Microsoft\\Outlook. They are not intended to be backed up or moved because they are just a cache of server data.
3. To reduce mailbox size or create local archives, Outlook supports exporting items to a .pst file (for example, to archive older items or back up data). This is the supported method to get data into a .pst file rather than converting an .ost file directly.
4. Large .pst/.ost files (especially above 25 GB) can cause performance issues and may hit size limits configured via registry (MaxFileSize / MaxLargeFileSize, WarnFileSize / WarnLargeFileSize). For very large data sets like 76 GB, it is recommended to manage size by archiving or splitting data rather than pushing a single file beyond recommended limits.

Because the context does not describe any Microsoft‑documented method or supported third‑party tool to convert a 76 GB .ost file directly into a .pst file, only the general, supported handling of .pst/.ost files and size limits can be stated.

References:

• Create an Outlook Data File (.pst) to save your information
• Configure the size limit for both (.pst) and (.ost) files in Outlook
• How to troubleshoot performance issues in Outlook