How to open an OST File in Office 365?

#1

An OST file (Offline Storage Table) is a local copy of your mailbox stored on your computer. It allows you to access your email, calendar, and contacts offline and make changes that will sync with the Exchange server the next time you connect. If you are using Regain OST to Office 365 Migration Tool, you can open an OST file by following these steps:

  1. Access Outlook and navigate the “File” tab in the top left corner.
  2. From the “Account Information” section, click on the “Account Settings” button.
  3. From the “Account Settings” window, select the “Data Files” tab.
  4. Click the “Add” button to open the “Open Outlook Data File” window.
  5. Please navigate to the location of the OST file on your computer and select it.
  6. Click “Open” to add the OST file to Outlook.

Note: If the OST file is password-protected, you must enter the password before it opens.

Once you import the OST file to Outlook, you can access the email, calendar, and contacts stored in it, just like any other email account.

Get more detail visit this post - Import offline OST to Office 365

#3

To open an OST File in Office 365 is directly not possible. You can convert those OST files into PST format and then import that PST files into Office 365 account as that can be simple to do. For converting the OST files into PST format you can take help of GainTools OST to PST Converter application and simply convert the files safely in a few clicks. The user can use this tool on any Windows OS. Refer this article for more details: https://www.gaintools.com/blog/import-ost-to-office-365-with-emails-and-attachments/