What are Outlook PST Files and Why Use Them… or Not?


Just about everyone I speak with at work complains about the size of their corporate email account.  Normally it’s not a problem (but people still complain) because when a mailbox approaches its limit, most email servers (like Microsoft Exchange) will warn the user so they can clean up the mailbox before the server enforces their size limits by restricting send/receive from the server.

Now, this is all Fine and Dandy UNTIL…you go on vacation for a few days, those email size warnings come and go, and then bam! Your mailbox is full, and you can no longer send/receive the email from your mobile or even OWA (Outlook Web Access) for that matter. I’ve received the call a million times. My iPhone can’t send emails, help!

  • So, what to do?
  • Is there a solution to these insufficiently sized mailboxes?
  • What should I do before I go on vacation?

Now I introduce you to the infamous (according to IT) Outlook PST file.

What are Outlook .PST files?

  • Outlook Data Files or Microsoft Outlook .PST files (as they are more well known) can be created using Microsoft Outlook to move or copy Emails and Attachments from your Server Mailbox account to your local PC. Essentially, it’s a local Archive or Storage file you create to store Email and Attachments on your computer’s Hard Drive, USB Drive, or Server Share (depending on where you create and store it).

How much can you store in Outlook .PST files?

  • Before Outlook 2003/2007, .PST files could only store 2 Gigabytes of Email and Attachments.  With Outlook 2003 and Outlook 2007, the format changed allowing the .PST files to grow as needed to over 20 Gigabytes in size unless the default configuration is modified.
  • Honestly, don’t let them get 20 Gigs.  It’s a much better idea to keep your .PST files no larger than a few gigs. If you need more storage space, then create a new .PST file instead of creating huge .PST archives. The larger the .PST files get the greater chance of corruption and data loss (plus the harder it will be to back up the bad boys.)  You can attach as many .PST files to your Outlook Client as you need so just separate your email logically across multiple .PST files if you need to store more than a few GIGs of old email.
  • TIP – If you’re using .PST files to archive old emails, compress them after you copy all the old data into them. Email is usually just text, so it compresses VERY nicely.

How can I create Outlook .PST files?

Why use/create .PST files? Benefits?

Mailbox Size

  • Remember the first paragraph of this Article?  Most email administrators limit the size of Corporate mailboxes.  The bigger the Mailbox, the more disk space they need, the more they need to backup AND the more TIME they need to perform those backups.
  • If you’re an email packrat (like me), a 200 Megabyte mailbox just won’t cut it.  That’s where .PST files come in.  Just create a .PST file and drag and drop your email into it.  They work just like a regular mailbox folder in Outlook.  Drag and Drop.  It’s SIMPLE!   <Let me know if you need more help.  Just post your questions in our Forum>.
  • The latest versions of Windows Search indexes your mailbox AND all local .PST files (configurable) which allow for almost instant access to all emails via the search features built into Microsoft Outlook.

Backup and Disaster Recovery

  • If you don’t have (or trust) an email administrator who regularly performs backups of your email server, then copying your email (yes, you don’t need to MOVE mail to .PST files, you can copy it also) to a local .PST file is a fast and easy method to ensure your email is recoverable in a server DR scenario.


  • .PST files make email portable.  For instance, let’s say you want to move email from one mailbox to another.  For example, perhaps your changing jobs and want to bring some old email.  Or perhaps you’re changing host providers.  OR, maybe you want to copy your personal and work email to a .PST file, keep it on a small USB drive and keep it with you at all times.  Like I said, .PST files keep mail very portable.  And yes, so is a GMAIL account but this article is not about GMAIL :)


  • Did you know it’s almost impossible to track/audit whether your IT guy/department is reading your email?  Moving “Sensitive” or “Confidential” email off the Email / Exchange Server to a local .PST file adds a layer of security.
  • Note: Most IT departments have the ability to grab your .PST files without you knowing it right from your Hard Drive at work.  Because of this, applying additional security on your computer’s Hard Drive is essential.  I’ll write an article on this subject shortly but for now, take a look at article.  It’s a bit “GEEKY” so I’ll follow it up soon with an article that explains a few options for securing .PST files.

What are the downsides to using .PST files?

Remote Access

  • Once mail is moved into a .PST file, it will no longer be available on the server using remote access applications like OWA or Mobile phones which SYNC with your mailbox.  To access the email in the .PST files, you will need to use a full Microsoft Outlook Client.  A small USB drive can help in these situations. However, it’s still not as convenient as leaving email on the server.

People Won’t Like you, and it’s possible you could lose your job

  • .PST files over time (depending on how many emails you receive/keep) can take up A LOT of space on your local Computer or a Server Share, depending on where you store them.  IT guys hate anything that makes them work on anything unless it is building their resume, so putting a lot of data somewhere which will require them to buy more disk space upsets them.
  • Corporate Legal and most Records Management departments don’t like .PST files as they allow you the end-user to easily ignore or bypass corporate document retention/destruction policies.
  • Corporate Information Security teams also don’t like .PST files because if Legal ever asks them to recover data for a lawsuit or subpoena, .PST files can exasperate the cost and effort of the data recovery.

System & Brain Performance

  • The more email you have, the more email both you and your computer need to keep track of and process.
  • Because more emails and attachments get indexed by Windows Search (or some other email/system indexer), your index will be larger, AND your searches will take longer.

So, hopefully, I answered all your questions about Microsoft Outlook .PST files and covered some high-level Pros and Cons.  But in case I missed anything, please feel free to drop a comment or post your question in my .



  1. Jeff

    November 21, 2008 at 8:02 am

    They’re also prone to corruption, requiring a costly pst repair tool to fix them.

  2. Moog

    October 8, 2009 at 9:46 pm

    >> Did you know it’s almost impossible to track / audit if your IT guy/department is reading your email? Moving “Sensitive” or “Confidential” email off the Email / Exchange Server to a local .PST file adds a layer of security.

    It appears you work in IT but don’t seem to have a good understanding of why organizations have certain flows in place. Page has some great info, helpful .PST ref’s but relaying an opinion advising people to take a resource they don’t own (workplace email) and violate corporate policy for 99.737% of corp USA by making it unfindable does a disservice to people who find your site. A competent organization has a process to classify sensitive / confidential email that doesn’t involve risking termination by hiding a resource you don’t own from the place you’re receiving it at. And no, it’s not about the bourgie’s vs. proles; it is about mutual respect betw. you and your workplace. If you’re not going to give it, please don’t expect it. pax.

    • MrGroove

      October 9, 2009 at 12:57 am

      HI Moog and Welcome to the site! I appreciate your comments and feedback however I can’t say I agree with them. That being said, I like a thorough discussion which leads me to:

      Yes I have worked in IT and I would argue that I actually have a very firm grasp around the details of general IT, information security, corporate governance, data classification and data retention. All of these topics are actually my specialty from a professional level and if you would read my article again, you would see that although I list out the What, How, Why, Pro’s and Con’s, I never actually make any recommendations the reader should take in regards to using PST’s other than Size. I especially never hint upon data theft which I would argue is a far stretch from creating a PST on a corporate machine and storing corporate email there. Sending email home or storing it on a personal device (if not allowed per corporate policy) yeah.. different story.

      In regards to your comment:
      “RE: A competent organization has a process to classify sensitive / confidential email that doesn’t involve risking termination by hiding a resource you don’t own from the place you’re receiving it at.”
      I applaud any Organization who actually takes the time to build a process to classify sensitive / confidential email or any data for that matter. I’ve written several myself…. The problem however is the “process” is doomed to fail even before it begins. Why? Well first, you need to identify all types of corporate data and (not just email) and assign it to your data classification and data retention model. Depending on the size of the “competent organization” that should only take…. a year or two…. or three… After all, before you can classify the data you must first identify all the data, the data owners, train them, coordinate them, argue with them, let them argue with legal rebuild your classification and data retention model again after the consultants leave because a new law was just passed with new mandates around data retention then the game starts all over again.

      So now that you have all the data identified, owners identified, data classified w/retention now the fun begins. Now you get to decide if you can enforce the new policy with technology or if you need to get the employees involved or both. In almost all cases it will be both which means now you need to train HR or some team to do a world wide tour and train the employees (or do CBT.. Hey, how about groovyPost!!!) or some sort of Corporate Policy training software/program/process (which no one will watch or they will but not really…). Then you will need to interview all the employees to discover all the workflows because Sally in accounting has a Boss who told her she can work from home on Friday but he read on the internet it’s not safe to email work home so she puts it on a USB drive, takes it home and puts it on her home computer where it stays…. and then there’s that guy who uses Microsoft Skydrive you didn’t know about and the other guy with a blog….. But that’s OK. You can just tell the auditors your a “Competent Corporation” and you’ve done your due diligence and writing a Policy and communicated the policy and all your employees have checked the box that says they are following the policy (but we all know they aren’t including the auditor)…. ohh.. what a game.

      Anyway, so once all the hard work is done, people are trained, Legal or the Records Management Dept. (whatever you name them) will realize that as great as the “process” is, it will be impossible to enforce it so they will just sign a big contract with Iron Mountain to Archive their Soft Copies and Hard Copies of everything, send emails to employees about not sending personal email, communicate the email destruction policies then just archive email and outlaw .pst files (if they get this far) and realize OMG… this is a really expensive waste of time wasn’t it BUT, the Auditors and Legal are happy (I think?).

      So yeah, I understand it and no, it’s not as simple as saying just write a policy and follow the process like any good “competent organization” should/does do. Respect? I wish it were that easy. I won’t even get into the Gartner stats that 1 out of ever 3000 (or is it 5000) employees are working for the competition…..

      It’s all about being informed, do your best to follow your corporate guidelines and never let your IT guys push you around. They work for you, not the other way around. If using a .PST can help you and it’s not against your corporate policy, great! That’s what this article is here for. To educate you.

  3. Clementine Avitabile

    July 28, 2010 at 5:27 am

    Interesting share man Thank you

    • MrGroove

      August 3, 2010 at 12:13 am

      Thnx. Many people are confused with PST files and Outlook. Glad it helped you out!

  4. Bart

    September 15, 2010 at 1:57 am

    Awesome! Simple and to the point. Thanks very much for the concise explanation!

  5. Kiran Parmar

    September 21, 2010 at 2:54 am

    Nice Post!
    I finally got what is pst for and how to use it!

    I have also got a few questions:
    1. Is it possible to somehow make a rule that whenever a mail arrives in my inbox, directly copy it to my pst file on the disk, instead of me manually doing it everytime?

    2. If the above is possible, then another case is that, I may not always have outlook running, so probably nothing would be copied to the pst file. So, in this case, the new mails should be copied when I start outlook the next time..

    Please let me know soon.
    Thank you for your time.

  6. Adela

    January 8, 2012 at 9:48 am

    I added a password to access pst folders and now I can’t remember it…is there a quick fix to this?

    • Steve Krause

      January 8, 2012 at 10:20 am

      Good/Bad News I guess is Outlook doesn’t use strong encryption on the passwords used on PST files so there is software you can buy to break into the PST.

      Unfortunately the last time searched Google for the software I couldn’t find a free version so I had to buy it. I went with Lostpassword.com as it’s been a credible company for a long time vs. some of the fly-by-night shady sites out there.

      Hope that helps!

  7. Andrew Cirel

    May 31, 2012 at 4:55 am

    When Outlook opens a PST file it reads it from begining to end (more than once). If this PST file is 20GB in size and is on a file server share it will empty the memory file cache on the server of all the millions of small files (e.g. spreadsheets) that users access. When your users then want to access their spreadsheet it is loaded from file server disk rather than memory – much slower. Companies which have file server performance issues always have very large PSTs or Access databases on their file servers, i.e. these very large files make your file server cache impotent!
    Let your emails be managed by an email server and your databases be managed by a SQL server – if you care about file server performance that is…

  8. -cj

    March 4, 2019 at 9:31 am

    Nice writeup.
    I was looking for the answer to when Outlook uses a .pst file. That is, for what kinds of accounts will outlook automatically store email in a .pst file?
    I’m guessing it has to do with whether the account/connection is POP or IMAP?
    But my memory is too rusty. My hotmail.com and outlook.com accounts store their email in online servers. Outlook creates an .ost file for them, which can be trashed/recreated because the data are on the server.
    But what won’t do that? What makes Outlook put mail in it Outlook.pst file? An ISP-provided email account which just holds email until my client (outlook) requests and stores it? That is, services that only support POP or any that are connected via POP?

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