OST files are Outlook offline data files automatically created by MS Outlook email client for offline data access and backup. This file syncs and stores all emails, mailboxes, contacts, calendars, tasks, notes, journals, etc from your email account.
If you have one or more OST files from an old computer and want to access it another computer with the latest version of Outlook 2019, then you need to convert OST to PST file because there is not any way to directly import OST file in any version of MS Outlook application.
PST file is also an Outlook data file format which is easily importable in all Microsoft Outlook editions including 2019. You can convert import PST file in Outlook using Import/Export wizard.
For a safe, easy and quick conversion of OST file to PST format you can use vMail OST to PST Converter.