Outlook PST vs OST vs OLM – What’s the Difference?

Summary: Know the difference between Outlook PST vs OST vs OLM. The PST is a dataset that allows backups and transfers. The OST is a dataset that allows offline access to Outlook. The OLM is a macOS-exclusive PST. If you want to migrate from OLM to PST, the most reliable way to do it is through third-party software. 

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Microsoft outlook

If you are a business user, there is a good chance that you are using Outlook.

Microsoft Outlook is a client that is most commonly used to access:

  • outlook.com
  • Microsoft Exchange accounts
  • and Microsoft office 365

but it is much more than just an email manager. MS Outlook is an email manager, task scheduler, calendar, and contact registry, all rolled into one.

What is the purpose of PST, OST, and OLM files? 

That said, you can indeed also use Outlook with other email providers, such as Google’s offering, Gmail.  Now, to offer the user all of these functionalities, the operating systems that Outlook runs on must be considered, and their utilities too. To offer a seamless cross-platform experience, these separate file formats need to be created.

The Outlook client is available for download on many versions of Android, iOS, macOS, and of course, Windows.

In this article, you will learn about the various types of information storage formats within Outlook, and their differences (e.g. difference between ost and pst in Microsoft Outlook), and you will also learn about another, lesser-known format called OLM.

To begin, let us learn about what these formats [PST vs OST vs OLM] are, and why we need them.

1Account SpecificNo


2Encompasses Full OutlookYesNo

3Created AutomaticallyYesYesNo

account setttings pst

To access these files, open outlook, click the “file” tab”, click “account settings”, click “account settings” again in the drop down menu, and navigate to “data files”.

This will show you the number of data files you have (OST, OLM, PST, etc) and also their storage paths.

Also Read: Top Solution to Repair Corrupt PST Files – With Stellar Repair for Outlook

What is a PST File?

PST is short for “Personal Storage Table” and is the primary Outlook Data File that is used when these file formats come into play.

The personal storage table (PST) is a data log that contains all of your personal information, such as the following:
  • All of your calendared events and items.
  • The entirety of your contact registry.
  • All of your sent and received email messages.
  • Any other information that you may have in Outlook, such as Tasks and To-Do lists.

Your personal storage table is housed locally on the machine that it is created on, and it is this very file that allows us to secure our Outlook data in case something goes awry.

Note: This will not include conversations and threads that you have chosen to “ignore”, and the hilarious reason behind the “ignore” option existing at all is given here, on the MS exchange team blog.

Anyway, this personal storage table can be used to do much more than just access your outlook mailboxes and events offline. The PST can be imported, exported, and transferred between hosts, with certain PST vs OST differences (such as transferability).

Also Read: Outlook PST File Not Found: 3 Solutions

In fact, this very table is what MS Outlook uses to create backups and restore them. The PST can even be used to transfer Outlook from one device to another.

Files with the .PST extension have inter-Operating system compatibility too, which is why you can import a . PST file into MS Outlook for Mac, from Windows. (We’ll get more into this in the Outlook OLM vs PST and PST vs OST difference sections).

The main PST vs OST difference is that the PST files are much more versatile than the OST files.

Also Read: Easy & Quick Ways to Fix Outlook PST Error 0X80040116

What is an OST File?

The term “OST” is short for “Offline Storage Table”.

What is the PST vs OST difference in files? Well, the OST is essential, at the roots of the matter, a personal storage table without the flexibility that a PST offers.

Also Read: How to Fix OST Error “File Access is Denied”?

The OST, as the name suggests, allows users to access their Outlook data even when they are not connected to the internet.

When you re-establish a connection between your machine and the internet again, the OST file will scan and compare itself with your current Outlook account, and then proceed to update your account with any changes that it finds.

Another PST vs OST difference is that the OST file is given weightage over the Outlook account.

What this means is that if there were changes to the OST file (when the device was disconnected from the internet), then those changes will reflect in your Outlook account.

When connected to the internet, however, the OST simply mirrors your Outlook account and creates save points along the way. As you read before, the main PST vs OST difference lies in the versatility of these two files.

Cosmetically, the PST vs OST difference is negligible, but functionally, only the PST will allow for transfers of the host device.

PST vs OST difference

The steps to creating an OLM file: Navigate to File > Export, and ensure that all the items in the pop-up box (highlighted in red) are selected; then hit the “ continue” button in the bottom left of the pop-up window.

If you want to import a file to Outlook for Mac (PST OLM, or from an older version of outlook on the same Mac), then the process is just as simple.


To import, navigate to File> Import, and then select the appropriate file type. Then, navigate to where the file is, and click “import”.

What is an OLM File?

“OLM” is the acronym for “Outlook for Mac”, and is basically a macOS-exclusive personal storage table. Why OLM files are needed, will come to them further down in the article.

A side note to this is that it is hard to transfer files using an OLM, as they cannot be transferred from macOS to any other operating system — only .PST files allow such a move.

However, you can use third-party utilities that is Stellar converter for OLM to convert. OLM files into .PST files, but we’ll come to that later.

Also, when we talk about Outlook OLM vs PST, the PST is much more flexible than the OLM, as .OLM files are only used for inter-macOS transfers.

This can prove to be a rather sticky situation if you want to transfer your Outlook for macOS to another device, say Windows.

How to Convert OLM files to PST files?

As we said, the safest (and easiest) way to convert OLM to PST is to utilize readily available third-party utilities such as this converter for OLM  by Stellar Data Recovery.

Below is a demonstration of the Stellar converter for OLM, but most converters will work in a similar manner.

In the instance of the example we are giving you, your OLM converter will process all relevant OLM items, such as:

  • emails
  • contacts
  • messages
  • attachments and more

With the advanced stellar converter for OLM, you will be able to export OLM files not only to a personal storage table but also to EML and MSG file formats, to be used as required. If you upgrade to the tech version, you will also be able to export your OLM mailbox(es) to Microsoft 365, PDF, RTF, and HTML formats.

The tool that we have linked to does have a free version trial that will allow the user to get a preview of their emails (including the “to”, “From”, CC, and BCC). The converter will allow you to migrate from Outlook Mac to Outlook Windows, and will also come in extremely handy if you need your emails in HTML or PDF form. It also has a feature called “browse” that will automatically list all the OLM files it finds in the search area, which comes in handy if you have multiple OLM files on your system.

Here are a few helpful links for you: [PST vs OST vs OLM]


The beauty of such tools lies in their simplicity: a few clicks and you’re done. Here is the process:


Step One: Download the OLM to PST converter and Run it. Now, Browse the location of your OLM file, or click “Find” if you do not know where it is.

OLM file

Step Two: Select the OLM file, and click convert in the bottom right of the dialog box that pops up.

OST files to PST

Step Three: Let the software generate your PST file for you. That’s it; you’re done. You have converted your OST files to PST, and these are now available for use.

Pro tip: This converter and others like it can often convert OLM to other popular formats too, such as MSG and ELM formats.

Things to Remember: PST vs OST vs OLM

It will hold you in good stead if you remember the following notes:

  1. OLM can not be used to transfer Outlook accounts to Windows.
  2. OST files can only be used for the specific account they were created for, and not for the entire Outlook client (with multiple accounts).
  3. You can not move OST files to other Outlook installations, i.e. you can not Import OST files.
  4. OLM files are not created automatically — they are created at export.
  5. OLM files are for the entire Outlook client (they cannot just be for Account A).
  6. You can find your PST in the following directory for older versions of Outlook: [drive:\Users\user\AppData\Local\Microsoft\Outlook] and in [Documents\ Outlook Files] for newer installations. Large PST files in documents will slow down your OneDrive sync (windows), so clean these regularly. And now you know the difference between PST, OST, and OLM files.
    And you also know how to convert OLM to PST files.

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