Finding the best OST to PST converter

A quick internet search finds lots of tools that claim to import OST files into Outlook. Some are even free (or so they say) but which one is best? The best OST converter will recover your valuable mail without data loss. That’s exactly what Aid4Mail does. But what about the others?

Our research team identified at least 130 websites offering email conversion software (there are probably many more). Products from brands like SysTools, Advik, 4n6, Stellar, BitRecover, Kernel Data Recovery, Aryson, MailsDaddy, Shoviv. Almost all are from India and most are mediocre at best.

We tested dozens of these OST converter tools and the results were shockingly poor – missing emails, lost attachments, slow conversions, minimal documentation, deceptive marketing. SysTools OST to PST Converter failed to export anything at all, resulting in an empty PST file!

However, the worst offenders are products that initially appear to work but lose important data during conversion. Data that may not immediately be obvious like embedded content and email header fields (metadata).

So if those are the worst, let’s talk about the best.

But first, if you’re an eDiscovery or digital forensics professional, Aid4Mail offers powerful features beyond simple email conversion that can greatly benefit your work. Our Email eDiscovery and Email Forensics pages provide in-depth information on how Aid4Mail can streamline your projects with advanced search capabilities, email recovery, and more.

Aid4Mail is the most reliable way to convert OST files to PST

Aid4Mail is a professional email converter that prides itself on converting without data loss. It is user-friendly software for Windows and supports a large number of mailbox formats and email accounts. These include OST, PST, Outlook 365, and Gmail.

Aid4Mail is used in a variety of contexts, ranging from small-scale, single-file imports to large-scale migrations and long-term criminal investigations. Customers include some of the biggest-name Fortune 500 companies, government agencies and legal professionals around the world.

Aid4Mail Converter showing settings for an OST to PST conversion.

A free Aid4Mail trial is available to download, and you will find step-by-step instructions (with screenshots) in our How to convert OST to PST tutorial. There are three editions of Aid4Mail, with licenses at various price points. One is an affordable two-week license for single-use conversions.

Aid4Mail’s key features

Convert OST to PST with or without Outlook installed

Aid4Mail doesn’t need Outlook to convert your mail and can process offline OST files directly. However, if Outlook is installed, Aid4Mail can hook into it to optimize performance (up to 4x faster) and access additional metadata. Either way, your OST files will be faithfully exported to PST with the folder structure intact.

Preserve metadata including message status

Aid4Mail not only converts the content of an email message but also its metadata. This includes messages status flags: Unread, Read, Replied, etc. This information is often overlooked by competing products but can be crucial in an investigation or for maintaining archives for legal compliance.

Extract mail from orphaned OST files

An OST file no longer associated with its Outlook profile is an “orphan”. It can’t be opened by Microsoft Outlook. However, after conversion to PST with Aid4Mail, its mailbox data becomes accessible again. Not only to Outlook but to many other applications as well.

Recover lost email in damaged OST files

Unlike other products, when Aid4Mail encounters an error from a corrupt email, it doesn’t quit. Aid4Mail skips the problem item and continues with the rest of the mailbox, providing you with the most complete conversion possible.

Full control over the conversion process

Filter out unwanted mail, remove journaling envelopes, process incrementally, split and merge files, reconfigure folder structures, limit file sizes, inject additional metadata, customize with Python scripts, and more…

Batch-process a large number of OST files

Set up multiple OST conversions in Aid4Mail to merge them into one PST file, for example, or to use different filters on each. In Aid4Mail Investigator and Enterprise, you can even run the conversions simultaneously and unattended. This leaves you free to work on something else while Aid4Mail is processing.

Advanced features for forensics professionals

All the tools you need for preparing email evidence for legal proceedings, criminal investigations, litigation, compliance, auditing, or freedom of information (FOI) requests. Tools like recovering unpurged mail, advanced search and filter (including pre-acquisition), search lists, deduplication, file carving from disk images, Bates stamping, Python scripting, and more…

How Aid4Mail beats the competition

  • More reliable and accurate than competing tools
  • Up to 6x faster than other OST to PST converters
  • Detailed progress information and error reporting
  • Aid4Mail Trial has no time constraints or limits on the number of emails processed
  • Accessibility features: high-contrast display, zoom, keyboard-only operations
  • Detailed context-sensitive user guide and online tutorials
  • No false promises or deceptive marketing
  • Award-winning customer support in English
  • High-quality software from Switzerland made by perfectionists

Which Aid4Mail edition is right for you?

If you just want to convert an OST file to PST, then the affordable two-week Aid4Mail Converter license is perfect. If you regularly need to convert OST files, a one-year renewable license is more economical.

If you work in the field of digital forensics, consider Aid4Mail Investigator your tool of choice. It’s not just a great OST recovery tool, but can also be used to collect mail from a large number of mailbox formats and email service-providers. And it offers powerful tools to filter out unwanted emails and remove duplicates.

Go to Pricing

Try Aid4Mail for free – no commitment

There’s lots more in Aid4Mail! The best way to discover its capabilities is to try it out. Download the free trial version now, there’s no time limit and no obligations.

Go to Downloads

For a detailed feature comparison between the three Aid4Mail editions, see the Aid4Mail 5 feature comparison table in PDF format.

What makes Aid4Mail so good?

We have been developing software since 1990. Our first email tool was launched in 1999 and Aid4Mail followed in 2005. Our experience in processing email data spans over two decades.

All core functionality in Aid4Mail is developed in-house. Key features are tightly integrated and optimized for speed. We are in full control of our code, including major components like email parsing and conversion, the filter engine and its search syntax, MAPI access to Outlook accounts, and even the IMAP protocol used to connect to services like Yahoo! Mail and AOL.

Important clients around the world rely on our software. These include US government and law enforcement agencies, top law firms, national libraries, prestigious universities, major banks, and international NGOs. Currently, half of Fortune 50 companies are Aid4Mail customers.

Aid4Mail is Swiss Made and meets the high-quality standards that Switzerland is famous for.

Details of our research into email conversion software

Where in the world were the products from? Of the 130 sites we investigated, here’s the breakdown:

  • 120 from India
  • 5 from Russia
  • 3 from the USA
  • 1 from Bulgaria
  • 1 from Switzerland (Aid4Mail)

Many of the companies making these products use deceptive marketing techniques. This is something we refuse to do as a company. For example, we found:

  • Multiple duplicates of the same tool, branded with different product names and, supposedly, from different companies. Doing this enables them to saturate search-engine results with volume of content.
  • Product websites that contain fake ratings, awards, reviews and customer testimonials. How do we know they’re fake? For example, when a customer’s photo appears multiple times on the same site using different names! Sometimes we found their real identity on another website. Presumably, these people are not aware of their identity theft.
  • Fake mailing addresses: Companies like to appear American when they’re not and so falsify their mailing addresses. We noticed because the same US mailing address was used by multiple companies that we knew were all Indian. Searching the address on the map showed no trace of any of these companies.
  • Fantasy office photos: Not only are the addresses falsified but the office photos too. Again, we noticed because the same address on multiple sites showed very different buildings. Nice buildings! Searching the map showed a very different situation.
  • Offers of “free software” that are not what they claim. Instead they’re trial versions with limited functionality that require a purchase to unlock their features. Aid4Mail also has a free trial but we do not claim it’s a free product. Aid4Mail is a commercial product and the trial is to let you evaluate the software, not to trick you into purchasing.
  • False promises: Refund policies that are so strict they’re almost impossible to obtain. For example, SysTools’ 30 Days Money Back Guarantee. Rest assured that’s not the case with Aid4Mail. We put our customers first.


What is an OST file?

A Microsoft Outlook data file used by the Windows version of Outlook. It stores offline data from an Exchange server or Microsoft 365 (formerly Office 365), or IMAP account. OST files act as local storage to speed up mailbox access and reduce bandwidth usage. By default, they only contain messages that are less than a year old.

What is an “orphan” OST file?

OST files in MS Outlook must be associated with an Outlook profile. A stand-alone OST file, no longer associated with its profile, is known as an orphan. It cannot be opened by Outlook so its data has become inaccessible.

What is a PST file?

A Microsoft Outlook data file used by the Windows version of Outlook to backup data. In older versions of Outlook, PST files were used for offline storage (as OST files are now) and are still used to store local POP account data.

How are PST files useful?

PST files can be imported into Microsoft Outlook even when not associated with an Outlook account. They can also be imported into Outlook for Mac and are supported by a variety of other email-related applications.

Why convert an OST file to the PST format?

There are 2 main reasons:

  1. Converting an orphan OST file to PST makes its email data accessible to Outlook again.
  2. The versatility of PST files makes them ideal for backing-up Outlook data, long-term archiving and data-exchange.

How to convert an Outlook OST file to PST?

Please follow the step-by-step instructions in our How to convert OST to PST tutorial.

Are PST files widely used?

Yes! PST is the most common target format among Aid4Mail customers. PST files are used in:

  • Business
  • Education
  • Government
  • Forensic and investigative work
  • Litigation
  • And more…

What is Aid4Mail?

Aid4Mail is a user-friendly Windows application that specializes in processing email: converting it from one format to another, searching it, and exporting it in useful ways.

Why use Aid4Mail to export OST to PST?

There are a few manual methods to convert an OST file. Aid4Mail stands out from the crowd because its conversions are reliable and avoid data loss. Aid4Mail can recover mail from an OST, even if it’s damaged. And it can export to a whole range of file formats, email applications and services.

Can Aid4Mail convert large OST files?

Yes! Aid4Mail can reliably convert large OST files and can even split them into multiple, smaller PST files. Aid4Mail can also process large batches of OST files. In the Investigator and Enterprise editions, Aid4Mail can even run them simultaneously and unattended!

Where can I get Aid4Mail?

You can download a free trial of Aid4Mail from our downloads page. Licenses can be purchased from our online store.

Where can I get help?

Aid4Mail is installed with a very comprehensive, context-sensitive user guide. Just press the F1 key while using Aid4Mail to open it. Alternatively, you can download the PDF version.

There’s also a whole range of tutorials and knowledge base articles on our website. If you’re still stuck, contact our award-winning Helpdesk.

About Fookes Software

Fookes Software Ltd
La Petite Fin 27
1637 Charmey (en Gruyère)

For over 25 years we have been developing award-winning tools and productivity software. We also have more than 20 years of expertise in the field of email processing and analysis.

Our clients include Fortune 500 companies, government agencies, law firms, universities, and professionals specializing in e-discovery and forensics from around the world.

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