My advice to customers who want to use PST files in their environment is pretty simple – don’t. Aside from the fact that PST files have no built in governance or information protection features (except setting a password), any organization using Exchange Online should have more than enough storage available between primary and archive mailboxes to store key data for as long as they want. Organizations using Exchange On-Premises would be better served adding additional storage to their environment or looking at Exchange Online Archiving to ensure they retain legacy data in a secure way that is easily searchable.
Even with the plethora of reasons to not use PST files, they are still a bad habit in a lot of organizations and often contain business critical data. This data, due to the nature of PST files is often sitting on a end user device and not backed up. Once that device dies, so too do the PSTs.
OneDrive & SharePoint as a “Backup”
Over the years, I’ve seen some clever users who have either been bitten by losing PST files from an old machine or who have recognized the lack of protection and have moved their PST files into OneDrive or SharePoint Online. This sounds like a great idea as the files are then “Backed Up” should the machine ever die. Unfortunately, the problem with this process comes with one of the best OneDrive / SharePoint features, Versioning.
Every time a file is changed and saved in OneDrive or SharePoint, versioning creates a new copy of that file and saves the delta as a version. This is fantastic for something like Word documents where you may modify a file ten times and look to roll back to an earlier version, however with PST files, this is essentially creating a new version every time a PST is accessed. Add multiple PSTs on top of this and we start to see our users OneDrive storage dwindling. I’ve seen first hand users with 15 PST files which are consuming around 3TB of storage due to version history. This is a headache for admins, particularly during a migration as it’s not always obvious where the storage is being consumed.
New Retention Policy Capability
Coming August 2021, a new retention policy for PST files will be rolled out to tenants. This policy will automatically enforce a 30 day retention on all PST files in Document Libraries. This means that while a decent number of versions will be retained in case of accidental deletion from the PST files but PSTs will no longer build up the storage they consume over months and years. This policy will be automatically enabled for all OneDrive and SharePoint sites on August 16th 2021.
There is an option to ‘opt-out’ via the SharePoint Online Management Shell however this will only opt-out for existing libraries. Any new libraries created after August 16th will be subject to the new policy.
Summary
It’s important to be aware of this new policy and prepare for it if your organization relies on PST files. Personally I think it’s long overdue and admins need to address PST files sooner or later, this is a good opportunity to do that.
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Sean McAvinue 