If you want to open OST file in Outlook 365, so here I suggest you to get SysInspire OST to PST converter software. This tool can convert OST file into multiple file format such as OST to PST, EML, EMLX, Office 365, Yahoo Mail, Gmail,etc. It has a 10+ file format for conversion. It can convert corrupted OST file into PST file format. It has a demo version that can allow users to convert 25 Items from each folder. It has technical support all users can get help by mail or live chat. It import mails with attachments such as photos, calendar, contects. Etc. It support all Windows OS. this tool does not require to install MS Outlook in users PCs to open OST file.
I was having trouble finding a solution to open OST file in Outlook 365 a few days ago when I came across eSoftTools OST to PST Converter software on the internet. It has many features, including email filtration, which allows you to filter their mail using dates. It can also convert your OST file to PST, Office 365, HTML, EML, EMLX, and other formats. It has a bulk conversion feature that lets you convert multiple OST files at once. It is compatible with all Windows operating systems and offers technical support via email or live chat 24 hours a day, seven days a week.