PST Migration Best Practices

Most large organizations are considering a data migration project to remove all PST files from their environment. PSTs ...

Most large organizations are considering a data migration project to remove all PST files from their environment. PSTs have been around for several decades and have always been plagued with problems relating to corruption, loss and theft. Regardless of how you’re going to embark on your PST file migration project, our blog will share with you our top 10 best practices to help make your project a success!

Key Takeaways

  • PST stands for Personal Storage Table, a file format created by Microsoft in the early 1990s for storage needs related to Microsoft Exchange Server
  • PST files were intended to prevent end-users from receiving "mailbox approaching quota" warning emails, but have been plagued with problems of corruption, loss, and theft
  • They were not meant for long-term storage, and can cause problems for remote and hybrid workers, and they are not compatible with mobile versions of Microsoft Outlook
  • Organizations are considering a PST migration, which involves eliminating PST files and ingesting the data into a target cloud platform like Microsoft Office 365
  • After a PST migration, organizations usually disable the ability for the Microsoft Outlook desktop/laptop client to access and create new PST files to prevent future issues

What is a PST File?

Best Practice - Text in Blue Color on Dark Digital Background.Let’s start with the basics: Some people might be wondering what PST stands for. It stands for personal storage table. This file format was created by Microsoft in the early 1990s to address storage needs relating to Microsoft Exchange Server. Many organizations were struggling with end-users wanting more mailbox storage space. Users would create a PST file on their desktop computer and drag and drop emails from their mailbox into the PST file.

The underlying problem was that end-users had very small mailbox quotas, but already people were starting to send larger and larger emails with attachments and other important information in them. So, the PST file tried to prevent end-users from receiving the infamous ‘mailbox approaching quota’ warning emails.

The PST file format changed a few times over the years, mainly to offer more space. However, almost from the outset, PST files had problems with intermittent corruption. This was especially true when people stored the PST files they needed on either removable media or network storage.

In addition, end-users regularly created multiple copies of ‘similar’ PST data files. This essentially was to have a copy of the PST in case the original became corrupt.

Problems have plagued the use of the files. Most people that have been around Windows or Apple Mac computers in a corporate environment will have stories to tell of problems with PST files over the years.

A final point to note about PST files is that they are very different to the OST file format. This is also a Microsoft file format used by Microsoft Outlook, but it’s not something that end-users interact with it. Instead, it’s the cache that Outlook creates of emails stored in Exchange or Exchange Online.

A lot has changed in the years after they were originally created, and now PST files are considered a high risk to many enterprise-sized organizations.

PSTs were never meant for long-term storage, despite how end-users used (and abused) them. Even Microsoft says they shouldn’t be used for long-term storage of messages. There are many problems with PST files; here are a few:

  • Likelihood of corruption. Particularly when stored and used from network locations
  • Multiple ‘backup’ copies on many different devices and removable media.
  • Difficult for end-users to find required emails; search often takes time to index newly added large PST files
  • High risk to the organization of PSTs on removable media being lost or stolen
  • Causes problems for remote and (especially) hybrid workers
  • Not compatible with mobile (tablet or smartphone) versions of Microsoft Outlook. PST files cannot be attached to Outlook or accessed.
  • Hard for legal teams to perform effective eDiscovery

Since there are so many issues with PST files, most organizations are considering a PST migration.

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What is a PST File Migration?

A PST migration means that the PST files that end-users have grown to love and hate over the years will be eliminated.  They will no longer need to remember which USB drive they have a copy of an old PST file on, and they’ll no longer see Outlook with multiple PST file entries in it.

Some or all the data from those PST files is usually ingested into a target cloud platform like Microsoft Office 365; we’ve never seen an organization simply prevent PST files and stop using them that way.

Following a PST migration, most organizations then disable the ability for the Microsoft Outlook desktop/laptop client to access and create new PST files. This is an essential step; otherwise, in a few years, users will have created new PST files and recreated the original problem.

Entering a PST migration project is not something to be done lightly. There is a lot of planning and work that needs to be done to successfully complete such a project, especially in a large global organization.

10 Best Practices for PST Migration

Regardless of whether your organization will perform a manual migration or take the often more robust and appropriate route of using a PST file migration product (such as PSTComplete) there are many things to consider. We’ve been migrating PST files for large enterprise customers globally for many years.

While every project is different and has unique characteristics and challenges that must be overcome, here are our ten recommended best practices for a PST file migration.

1.     Identify All Your PST files

There are at least two ways that you can discover PST files in your organization, as they’re likely to be stored in two places:

  1. Network Shares
  2. Local Hard Drives 

Let’s look at each location in turn:

Network Shares

As mentioned in this blog and other blogs on our site, end-users typically make multiple backup copies of PST files. A great place, in their mind, is to put those copies on network shares. End-users put the PST files on their home drive, or a shared network drive used by their department or team.

These can be relatively easy to scan from a workstation that can attach to the same network storage using an account that has permission to read from all the folders on the storage.

Usually, with little or no impact, a list of files, locations and sizes can be obtained. This list will give you and your project team an overall idea of how many PST files there are, when they were modified, where they are located, and the size of them.

You can do a little more analysis of the PSTs on network shares by putting the data you collect from the scans in Excel. You might be able to see a particular folder that has many PSTs in it, and you might be able to see the same PST file name in multiple locations.

This analysis will help you understand part of the overall scope of the PST migration.

It might also help you see that further into the project, some or all these PSTs might have ownership challenges associated with them. For example, a PST file in the Sales network share might belong to any one of the current members of your sales team, or it could belong to a former employee. In some organizations talking to the department or team that use a network share might help resolve ownership issues before starting the PST migration project.

Local Hard Drives

Local hard drives can be trickier to scan.

What we’re really after here is both the files on local hard drives and removable media. Ideally, these might be part of a single user's Microsoft Outlook profile, which makes it easier for a third-party PST file migration solution to accurate assess who owns a particular PST file and to initially find it.

It’s likely that PST files attached to an Outlook profile will be unique for that user, but that the user might have other ‘backup’ copies of that same PST file stored both locally and on network storage.

On shared PCs, there might be multiple Windows and Outlook profiles which should be assessed if possible.

2.     Decide On A Migration Strategy

It’s important to build a robust migration strategy. It’s the place where all the planning should be described, along with decisions about the migration and issue or problem resolution procedures. Also in the strategy should be information about the proposed migration timetable. Finally, you should decide if users are going to be involved in the migration, or whether all the discovered PST files are going to be migrated without involvement. 

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3.     What Is Your Target Platform?

When deciding on a PST file migration, obviously, an important consideration is where the data will be migrated to. The usual choices are:

  • On-premise Microsoft Exchange mailbox
  • Office 365 mailbox or Office 365 personal archive

If the migration is going to move a large amount of data to a mailbox, consider that Outlook caches that data locally (meaning a significant download of data might occur the first time a user connects to Outlook). This means that when there are storage limits in place, they might be exceeded when the data import is large.

Many organizations migrate the PST file data to the Office 365 personal archive, but that relies on the user having a license to use that feature. Note: It’s possible to do this when using Office 365 Hybrid; even if the mailbox is stored on an on-premises Exchange Server, the personal archive can be remote. 

4.     Choose a Migration Method

For most organizations, there are two choices when it comes to choosing a migration method:

  • Manual
  • Third-party product/solution

Let’s look at each in turn:


A manual PST file migration could involve users dragging and dropping their data into their main Outlook profile, i.e. their mailbox. Many organizations enable a personal archive mailbox for users to store, or instead for them to archive, older emails.

With this approach, users can flexibly move data to where they think they might make the most use of it. However, there are several drawbacks to this approach. For example, many users will try dragging and dropping huge amounts of data into their mailbox, bringing back those emails about the mailbox quota being reached.

Another option is to use the Microsoft Import tool and put the data into Azure storage, or ship data drives to Microsoft. This is usually an IT-led approach and, unfortunately, is tricky to manage and leads to end-users getting interrupted access to their data in many cases.

The IT team also needs to create a PST mapping file (to map the file name to a specific user), create a PST import job, and optionally filter some of the data and then perform the import.

This takes some time, and if you use the drive shipping method, it can take quite some time and adds the expense and difficulty of using removable media.

Doing a manual PST migration only works for small PST file migrations. Therefore, most enterprise-sized organizations need an automated approach. This is where third-party solutions come in, as we will see in the next section.

Third-Party Product/Solution

A third-party product/solution will help perform an enterprise-sized PST file migration for you and your organization. There is typically a lot of automation involved as well as project governance, reporting and auditing.

As mentioned in the previous section, manual PST file migration methods typically only work for very small migration projects. For almost every other type of migration, we recommend a third-party product/solution to help manage and perform the migration.

5.     Why Use a Third-Party PST File Migration Tool

We recommend using a third-party PST file migration tool. Here are some of the reasons why:

Governance and Reporting Features

A third-party PST file migration tool should be able to easily handle the detail of handling each individual PST file, but it should also take a more comprehensive approach and provide you and your team with the tools needed to manage and report on a large-scale PST file migration with ease.

Complete Solution

As discussed in this article, copying data from a PST file into the chosen target is only part of the overall migration process. While that article talks about the steps involved in performing a legacy archive migration, there are many similarities when it comes to migrating PST files. There are many other tasks that might need to be performed as well as copying data, such as:

  • Enabling a personal archive mailbox
  • Changing message size limits
  • Removing PSTs from the Microsoft Outlook profile after the migration completes
  • Communicating with the end-user
  • Increasing the size of a mailbox (or personal archive)


If you’ve not heard of it before, review our blog on Service Protection Throttling. It’s essential to know about it when performing a large-scale migration project of any kind into Office 365.

A third-party migration tool should be able to handle the migration with maximum speed once it’s ramped up to production migration usage. Further, the product should use technology that allows for the scaling up and down of the migration environment on demand, with ease, as our PSTComplete solution does.

Least End-user Impact

Consideration should be given to users that might still need to access the PST data during any migration window. Will they be able to do that? If they can’t, then obviously the migration window for that user should be minimized as much as possible. Some solutions, like PSTComplete, allow end users to continue to access the data even during migration.

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6.     Make End-users Aware of the Upcoming Migration

At Cloudficient, we’ve helped many large organizations perform successful PST migrations. One of the topics which are often discussed is how to make end users more aware of what is happening with their PST file data.

Some of that data is closely guarded by end-users. It is often old emails from the early days at an organization; sometimes, it is even emails from previous organizations that may still have some use to the end-user in their role.  Telling users that that data is ‘going’, at least that’s how they might interpret it, is a difficult discussion to have.

We recommend you explain to users that the upcoming migration is to upgrade their PST files. Instead of end-users having to manually look after making backups and adding data, the upcoming migration will provide automated ways to do that. On top of that, the data will always be accessible, without the need to find that difficult-to-find USB drive from many years ago.

7.     What Happens with PSTs After Migration?

All organizations that go through a PST file migration don’t want to perform it more than once. Soon after and sometimes during the migration, changes will be made to prevent users from creating new PST files or opening/accessing old ones.

This prevents the problems of PST files from reoccurring in the future.

Most organizations will implement Group Policy Objects (GPOs) to: 

  • Stop end-users from creating new PST files
  • Stop end-users from accessing existing PST files

These GPOs will be applied to almost every machine, though there might still be some IT admin-type workstations that do not have this policy applied to them in case the need to export a mailbox to PST is required.

8.     Communication is Critical

As part of our workflow orchestration engine built into our ReMAD platform, we made a conscious decision to ensure that end-user communication is a big part of the workflows that are implemented.

If we customize those workflows for customers, we still stress how important it is for end-users to be kept informed of:

  • What will happen
  • When it will happen
  • What will happen afterwards
  • What to do if they encounter a problem

With those critical components included in a PST migration plan, it greatly helps end-users fully understand the process that their PST data files will go through. 

9.     Identify PST File Ownership

One of the important aspects of a PST migration is identifying the owners of all PST files that have been discovered.

Some will be easier than others: End-users know which files on their local machine are theirs and whether they want to keep them (or need any of the data from them). That gets more difficult on shared PCs which are found in some office locations. It gets more difficult again when PST files are discovered on network shares. And often, the trickiest is what to do with PST files that appear to have no owner.

An enterprise-ready third-party PST migration product, like PSTComplete, will help you at every step.

10.   Do a Proof of Concept 

As you’ve seen in the list in this article, there are many different things to consider when performing a PST file migration. Ultimately though, a vendor can assure you of how their product works and solves all the challenges that are unique to your organization and project. Still, the true test is using the product in your environment.

At Cloudficient, we always recommend doing a proof of concept. We’ll conduct a proof of concept at no cost, with no commitment, in your environment with your users and your data. During the proof of concept, settings can be configured to suit the needs of your environment. 

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In this blog, we’ve taken a deep dive into the ten best practices to adopt when your organization performs a PST file migration. Every PST file migration project is different and has unique challenges; however, if you and your organization take into account all of the things in this article, we feel sure you’ll be on the road to a successful migration project.

With unmatched next generation migration technology, Cloudficient is revolutionizing the way businesses retire legacy systems and transform their organization into the cloud. Our business constantly remains focused on client needs and creating product offerings that match them. We provide affordable services that are scalable, fast and seamless.

If you would like to learn more about how to bring Cloudficiency to your migration project, visit our website, or contact us.

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