To read your emails from .ost file created with IMAP, you need to use 3rd party IMAP OST to PST converter. You can checkout various ost to pst converter for IMAP emails from below listing :
I have personally tested and used all 3 converters and all works fine. Last ost converter has got rich features and you can get a good bundle license deal on respective website. Go ahead and test these converters on your .ost file and see conversion results. If you feel satisfied then order license for anyone of the converter and get your ost file converted to pst file, which can easily open in MS Outlook.