Organizing your Outlook email PST files

Have you ever seen the following message when booting up your computer? “To free up disk space, Outlook Express can compact messages. This may take up to a few minutes.” Do you use Microsoft’s Outlook email manager? If yes to both, you may be getting this message because your PST files have grown too large. Or if you have noticed that the performance of Outlook has started to suffer, you may also have an issue with your PST file size. But what is a PST file?

Intro to PST files

A PST file is a Microsoft Outlook file that contains emails and all other types of information that you work with in Outlook. If you want to know where this file is located on your hard drive, you can do a search for “*.pst,” or go into the Account Settings in Outlook (which is accessed differently depending on what version of Outlook you have, but it’s not too difficult to find) and select the Data Files tab to see all of the different PST files that Outlook is connected to. There will be a default file called Outlook.pst file, and if you have no experience working with PST files, this is likely the only file that will be listed. And odds are, it’s going to be HUGE, especially if you have been using Outlook to manage your emails for a while and you keep most of your emails. You can look at the size of the file(s) by selecting “Open File Location…” or navigating to the file location listed in Windows explorer.

Why you should care

You should not keep large amounts of data in your Outlook.pst file, as that can significantly degrade the performance of Outlook. If your Outlook.pst is over 2 GB, I highly recommend you archive all of the emails you want to keep in a different PST file. To create a new PST file:

  • From the Data Files tab, select “Add…” and follow the instructions, saving the new PST file in a location like “My Documents\Outlook_Mail_PSTs” so it’s easy to find later
  • Choose what name you would like the PST file to have when shown in Outlook
  • Once you see it in Outlook, you add category folders to it by right-clicking on the new PST in Outlook and selecting “New Folder.”

My organization system

I recommend starting a new PST file once a year (or more frequently if you get a lot of email, or every other year if you get relatively few emails). I do this at the start of every calendar year (which I find is nice because there is usually somewhat of a break in email traffic over the holidays), naming the file something like “Archive_2012.pst” and then giving it the same name in Outlook. Then I go into this PST directory and create all of the folders that I had in the previous year’s Archive directory that I believe I still need for the upcoming year. By starting a new PST file every year, I ensure that they won’t get too big. This also makes it very easy to see what PST files are the most recent and to port your PST archives into a new computer or account. Another great aspect of this system is that you can remove archive folders that you no longer need each year, so you don’t have ridiculous numbers of folders to look at every time you want to archive an email. Yet you don’t lose the folders that you used to organize your emails in previous years.

If you are facing a massive Outlook.pst file, it is certainly not too late for you! Just create a new PST file for every year (or multi-year periods if you think that will work) and move emails from those years into those new PST files. This is as simple as creating all of the folders you need in the PST files and doing some drag and drop in Outlook. Also remember to move your “Sent Items” emails from each year into your new PST files; that can be a huge amount of email that clogs your default Outlook.pst file.

So I moved everything over. Why is my PST file still huge?

After moving all of your archived emails into new PSTs, you may notice that your Outlook.pst file is still pretty huge. This is due to how Outlook manages memory within PST files. Outlook will reduce the size of this file after a while, but if you want that reduction immediately, double-click the PST in the Data Files tab and hit the “Compact Now” button. This may take a while though, depending on how large you let that PST file grow. And in my experience, it may not fully compact it the first time you try. If this happens, wait a little while and try again.


Also note that in some versions of Outlook, the PST directories are sorted alphabetically/numerically in the left frame of Outlook. So if you want them in particular order, you may need to modify the beginning of their names in Outlook. An easy solution to this is to add “1_”, “2_”, etc. to the beginnings of the names that appear in Outlook, which you can modify in the Data Files tab under Account Settings.

Other resources

There are many more great resources online that cover the fine details of how to manipulate these PST files. One of the best official sources is this Microsoft page. My primary goal is to show you why creating and using new PSTs to archive your email is so important, and how I organize my PSTs.


I taught this same subject to astronauts in a class called “Operations LAN (Local Area Network) Data Storage & Management,” when I was working in the Daily Operations Group (the DOG’s) at NASA’s Johnson Space Center (JSC). NASA loves acronyms. The astronauts learned how to manage their PST files when working on the laptops that are onboard the International Space Station (ISS). It is often said that the most precious resource on the ISS is crew time, and if NASA deems PST management important enough for astronauts onboard to spend their very precious time on, then you know it’s important!

Now you may be thinking, “I’m not an astronaut! If they need a full class to learn this stuff, how could I possibly learn it?” First of all, you need a higher opinion of yourself: you can learn the same things that they can! Second, it’s really not that hard. I taught this class when I was an undergraduate student. You just need to take a couple of minutes to figure it out, and after that you will enjoy much improved Outlook performance.

If you have any advice or questions regarding Outlook PST files, please feel free to share below.

One comment on “Organizing your Outlook email PST files
  1. Keith says:

    Great piece. I’ve always been sloppy bad with my PST files. Hadn’t thought of compartmentalizing based on CYs. Thanks!

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