You can all use this eSoftTools OST to PST converter software to import Outlook OST to Outlook.com. It easily imports OST files created from Outlook COM, Office 365, IMAP and Exchange servers to PST, Yahoo Mail, EML, EMLX, Office 365, PST, HTML and many more formats. It has a split PST file option, it splits large sized PST files into smaller sized PST files. You can try a free demo version to get some insight into how it works.

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