What's the difference between .ost and .pst files?

OST file is created when Outlook is configured with Exchagne Server and cache exchange mode is enabled.

If we configure Outlook with POP then PST file will be created.

For more information about ost and pst, plese visit the URL: https://www.tipsoverflow.com/what-is-difference-between-outlook-ost-and-pst-file-format/

OST is Offline Storage Table and PST is Personal Storage Table. You may also check out more details from this article written on the Difference Between OST and PST file. 

OST and PST both are different file formats. Outlook creates PST in stand-alone mode and OST with exchange server connectivity. If you have an OST file but, don't have Exchange server connectivity then, it is impossible to access OST file contents. To access OST file contents, you need to convert to the .pst file format.

For OST to PST conversion:

Visit: http://www.axblaze.com/products/osttopst-converter.html

Easily export offline OST data into Outlook PST file with the assistance of OST to PST Converter application that is made up by experts to recover and convert OST data file into PST data file. It deeply scans OST file and converts data into PST, EMLX, EML, MSG, HTML, vCal, vCard, and MBOX file format according to users requirement. This is a very famous software in the data recovery field. It is supportable to export encrypted and password protected file. Using it you can convert single mailbox as well as multiple mailboxes in a couple of clicks without facing any trouble. It gives 24x7 technical support.

Read More Info: https://ats-ost-to-pst-converter-toolkit.en.softonic.com/

If you are disconnected from Exchange Server or your Exchange Server is damaged, then you need a third-party OST to PST Converter Tool. With the help of this software, you can quickly move to your all-important data in just minutes.

For software download click here: http://www.sametools.com/convert/ost/

Outlook Data File (.pst)

A Personal Folders file (.pst) is an Outlook data file that stores your messages and other items on your computer. This is the most common file in which information in Outlook is saved by home users or in small organizations. Home users usually use an Internet service provider (ISP) to connect to the Internet. The ISP also provides one or more email accounts. The most common types of accounts are referred to by their Internet protocol names — POP3 and IMAP. Another type of account is an HTTP or web-based account that works similar to IMAP email accounts. All three account types use a .pst file.

Your items can also be moved or archived to an Outlook Data File (.pst). Because a .pst file is kept on your computer, it is not subject to mailbox size limits on the mail server. By moving items to a .pst file on your computer, you can free up storage space in the mailbox on your mail server. Outlook can be configured to deliver new items to a .pst file, but if you do this, it has several disadvantages. This includes being unable to work with your items when you are using Microsoft Outlook Web Access with the Exchange Server email account or when you are working on another computer.

Warning  Do not access an Outlook Data File (.pst) from a network share or another computer, because it increases the possibility of data loss.

Offline Outlook Data File (.ost)

Typically, when you use a Microsoft Exchange Server account, your email messages, calendar, and other items are delivered to and saved on the server. You can configure Outlook to keep a local copy of your items on your computer in an Outlook data file that is named an offline Outlook Data File (.ost). This allows you to use Cached Exchange Mode or to work offline when a connection to the Exchange computer may not be possible or wanted. The .ost file is synchronized with the Exchange computer when a connection is available.

Offline folders are replicas of the folders found in your mailbox on the computer that is running Microsoft Exchange. They make it possible to take a folder from a server location, work with the contents of the folder when you are not connected to the network, and then, when you are connected again, update the folder and its corresponding server folder to make the contents of both folders identical. This process is known as synchronizing folders.

You can add, delete, and change the contents of an offline folder exactly as you can for a folder on a server. For example, you can change and move items between folders, send messages that are included in your offline Outbox, and view the contents of your offline public folders. Meanwhile, new messages are kept in your Inbox on the server, and other people might add, delete, and change items in public folders. You’ll not be aware of these changes on the server until you synchronize.

The information that is synchronized includes the following:

• Headers: For email items only, a header is a descriptive identifier that provides the sender's name, the subject line of the message, the time when the message was received, and the size of the message.
• Full items: A full item includes the header, the body of the message, and any attachments, such as embedded objects or pictures.

When you work offline, folders that are synchronized are determined by Send/Receive groups. By using Send/Receive groups, you can choose which folders are synchronized and kept current so that when a connection to the server is not possible or you choose to work offline, you can continue to work with those items. You can also specify that updates to the Address Book be downloaded during synchronization.

If you use an Exchange Server email account, we recommend that you use Cached Exchange Mode. Most of the reasons to work offline are eliminated when you use Cached Exchange Mode. The lack of a network connection is almost transparent to you because you can continue to work with your items whether you are connected to the computer that is running Exchange.

By default, Cached Exchange Mode creates and uses an Offline Folder file (.ost) and then downloads and maintains a synchronized copy of the items in all folders in your mailbox. You work with the information on your computer, and Outlook synchronizes the information with the server. When your connection to the Exchange computer is interrupted, you can continue to work with your data. When a connection is restored, changes are automatically synchronized, and the folders and items on the server and on your computer are identical again.

With Cached Exchange Mode, you do not have to set up Send/Receive groups, choose folders that you want to be available offline, and then keep those folders synchronized.