Are you looking for a reliable and powerful solution to import your OST file to IMAP account then the only software that can do this is
eSoftTools OST to PST Converter Software. With its help, you can export OST files to IMAP accounts as well as to files like PST, EML, MSG, ELMX, MBOX, HTML, Zimbra, VCF, & ICS without any problem. In this tool, you also get the facility of email filtering, naming convention, and split features.
More info:- Import OST file to IMAP account