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In Outlook 2007, Unicode PST and OST files can grow up to 20 versions, and for Outlook 2010 and later versions, the limit increases to 50 GB.
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PST size: If you’re familiar with Outlook and have been using it since the beginning, you are probably aware that different Outlook versions have different PST size limits. Several factors prevent corruption and error in Outlook files, I’ve listed some of the factors that play a crucial role in the 0x80070021 error. How to keep PST files safe from error 0x80070021?
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