Summary – Storing of Exchange Mailbox data on the Cloud platform like Office 365 (Exchange Online) has many benefits. So here are the complete steps to resolve how to import OST file in Office 365 account issue. Read this article to perform this process in a quick and secure way. Looking to import OST file in Outlook 2019? Bad news is that OST cannot be imported technically, as PST can be. Good news is that you can convert the data in OST to PST and then import PST as usual.