I would recommend you to have a look here for once where they have mentioned some cool techniques to Resolve Error- “The data file is associated with a mail account OST” by using eSoftTools OST Recovery software. This tool also provides the features to split the PST data into smaller bits and also shows the preview of the conversion. This application supports all editions of MS Outlook.
Read More:- Resolve error- The data file is associated with a mail account OST
OST file used when user contact exchange server for email some times there are so many resign to corrupted exchange server and ost file is not used for user to view email dux data recovery ost to pst converter software on the best software to convert ost file data in to a pst file dux data recovery support all the version of the ost file. for more info https://www.duxdatarecovery.com/ost-to-pst-recovery.php