How to Archive Emails in Outlook – Office 365, Microsoft 2016. Allow me to explain how you can archive and organize outlook emails using the .PST file format.
An .OST file is an Outlook archive files used by Microsoft Outlook that allow you to work on your Microsoft Outlook when you are offline (from Wi-Fi or Internet connection). It is a default file created by Microsoft Outlook to store all you email.
A .PST file is a file created by the user (you!) in the Microsoft Outlook to organize and store your emails in your hard drive. The .PST file is essentially like and .OST file except that you can create multi of the.PST file while there can be only one .OST file per email account.