There are a number of ways for companies to practice email retention, including email archiving solutions and preservation policies. One method for Exchange Server users not recommended by experts is personal storage table files, or .PST files.

A .PST file is a file-access-driven method of message storage, according to Microsoft. That means the system uses special file access commands that the operating system provides to read and write data to the file.

These types of files are popular for Exchange Server users to avoid meeting the platform’s email inbox quotas. Users will convert files they wish to keep into .PST format in Microsoft Outlook and hold onto them for however long they are needed.

At first glance, it sounds like a reliable enough archiving strategy – files don’t clog users’ inboxes and are stored on the company’s local or network drives. But this may cause several major problems that will adversely affect the company, including failing to comply with email retention requirements and failing to be prepared for eDiscovery requests.

The following problems arise when users store emails in .PST files for long-term retention:

1. PST Files are not reliable

In fact, the method is so unreliable that Microsoft doesn’t recommend it practiced for email archiving. The company’s TechNet Performance Team posted an entry on its blog entitled “Network Stored PST Files … don’t do it.”

2. PST Files are vulnerable to data loss

A major issue is unintended data loss. Such files stored on a computer’s hard drive are usually without a backup. If a user’s computer is lost, stolen, hacked or the hard dive fails, the file will be lost forever.

3. PST Files can become corrupted

.PST files stored on a network drive are also vulnerable to data loss. Because the files are stored on the network, a user needs a network connection to access them, whether for eDiscovery or other purposes. According to Microsoft, “Microsoft Outlook tries to use the file commands to read from the file or write to the file, but the operating system then has to send those commands over the network because the file is not on the local computer.”

That process can’t happen should a network connection degrade or fail, which in turn will corrupt the .PST file and make it unreadable.

4. PST Files slow down the Network

Ironically, .PST files can be a common culprit behind the network slowdowns and stoppages that corrupt them. The size of a .PST file, compounded by the number of users that retain emails in such a way, places a lot of strain on a network, according to Microsoft.

In its Performance Team blog post, Microsoft gives the example of a couple hundred users who each had two or three, a low estimate, .PST files in Outlook. The users never delete the files and they continue to grow in size the longer they are stored.

Each time the user launches Outlook; the program makes a request for the two or three .PST files, which Microsoft estimates to be about 1 gigabyte each. When the 200 or so users launch outlook, that’s 600 gigabytes – 200 users, times three files each at 1 gigabyte each – worth of files being requested at once.

“That’s an awful lot of Disk & Network I/O to process simultaneously. This is a very common scenario – the file server ‘freezing’ for a few minutes at a time while it tries to service these requests,” according to Microsoft’s blog post.

5. No centralized storage of PST Files

Since PST files are stored on local drives, they can be lost and un-producible when the company faces litigation and an eDiscovery request. If so, a judge can levy sanctions and monetary fines for improper email archiving. On the flipside, PST Files can also suddenly show up when the company thought they had legitimately purged records according to their email retention policy rules.  With PST files residing on many different hard drives, it is hard to keep track of all the files and to know which data you have and which data you don’t have. It goes without saying that this uncertainty is less than desirable when dealing with an eDiscovery request.

In short, storing emails in PST files is simply not a good archiving strategy and a centralized email archiving system is advised instead.