How To Backup Microsoft Outlook OST File: 3 Ways to do it

Microsoft Outlook is one of the most popular emailing solutions on the market. In fact, it’s right behind Apple’s Mail and Google’s Gmail. As the name suggests, Outlook comes from one of the most recognizable brands in the world of IT – Microsoft.

There is one thing that is difficult to do with Microsoft Outlook though – many users find it hard to back up Outlook OST files. Below you can find three proven methods to back up an OST file and why you should do it. First, let’s see what exactly OST files are.

What Are OST Files?

Every software you use stores files on your drive under a specific extension. Some tools have entire extension lists. Microsoft Outlook is one of those tools which saves files under a range of extensions, and one of those extensions is .OST.

2026 Technical Update: 'New Outlook' vs. Classic OST

As of 2026, Microsoft has significantly transitioned users to the "New Outlook for Windows." Unlike the Classic version, the New Outlook is web-based and stores significantly less data in local OST files, relying instead on cloud-side caching. If you are using the New Outlook and cannot find a large OST file, your data is likely stored entirely on the Microsoft 365 server. Backup remains essential, however, to protect against account lockouts or server-side accidental deletions.

Now, the purpose of the OST file is to enable one specific Outlook capability. Thanks to OST files, you can continue your work in Outlook even when your Internet connection drops. If you have a slow or unstable internet connection, this Outlook’s feature enables you to use it efficiently.

Once the internet connection is established, the OST file connects with the Exchange server and synchronizes with the inbox.

Three Easy Methods for Backing Up OST Files

Now that you understand why knowing how to back up an OST file is important, here are three methods you can use to do it and reap all the above-listed benefits.

Method 1: Backup OST File Using Third-party Backup Software [Recommended]

While you will find three methods to back up OST files in this guide, it’s recommended that you use a third-party backup software like Wondershare UBackit. It offers unique advantages over other methods. Wondershare UBackit is simple to use, works extremely fast, can back up OST files automatically, and can encrypt your backups for increased security.

Wondershare UBackit - Your Reliable Email Backup Tool

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Back up emails to local hard drives or external storage devices effectively, safely, and completely.

Provide automatic backup to back up your email files daily, weekly, monthly, or non-stop.

Set a password to protect your backups, keeping your data confidential should it be stolen, lost, or compromised.

Support incremental backup, which saves only the changes made to your files since the last backup, reducing backup time and saving storage space.

Here is how to back up an OST file on Windows with this app after downloading and installing it on your device.

Once you click the Backup Button, UBackit will start the backup process. Wait for seconds to minutes depending on the file size.

Method 2: Backup OST File Using Microsoft Outlook

You can quickly back up an OST file using any Microsoft Outlook, including Outlook 365. Here’s what you need to do.

Method 3: Backup OST File by Converting OST to PST

Before we start with method three, you should know that PST files are Outlook Data Files. These files store various Outlook items, including the messages on your computer. However, this only applies to Outlook 2013 and earlier versions.

In Outlook 2016 and Outlook for Microsoft 365, your IMAP data is stored in OST files. If you need to back up OST to PST in Outlook 2016, follow the next steps. First, you need to download and install a proper tool. We’ve selected the Recovery Toolbox.

Benefits of Backing Up OST Files

So why go through the extra effort to back up an offline OST file? Here’s what you need to know. OST files are vital for Microsoft Outlook to work properly. OST files are prone to specific problems. For instance, OST files can fail to synchronize or authenticate correctly, or they can go corrupt and simply fail to synchronize what you’ve been doing in MS Outlook while you were offline.

If you decide to backup your Outlook OST files, you will unlock the following benefits:

Conclusion

As you can see, it’s not much of a challenge to back up an OST file now that you know what to do. It will help you keep your settings if the OST file gets corrupted. Most importantly, you can keep your email conversations safe with an OST backup file.

The easiest and most secure way is to use the Wondershare UBackit tool to back up an Outlook OST file. The other methods – using MS Outlook and converting OST to PST – will also work fine.