Last reviewed on November 11, 2014   —  44 Comments

Beginning with Outlook 2003, the new Unicode pst/ost format support much larger data files, with the default data file size set to 20 GB (Outlook 2003 or 2007) and 50 GB for Outlook 2010 or 2013. While this size is more than enough for most people, it can be raised in Outlook 2003/2007, if needed, by setting two registry values. The default file size in Outlook 2010/2013 of 50GB is currently the maximum recommended limit for Outlook 2003 and up.

Note: At this time, the maximum recommended ost or pst file size is 50GB.

Browse to HKEY_CURRENT_USER\Software\Microsoft\Office\xx.0\Outlook\PST (replacing xx with your version of Outlook: 14 for Outlook 2010, 12 for Outlook 2007, or 11 for Outlook 2003.)

Unicode pst format

For Unicode pst and ost files, create DWORD values of


Add the DWORD to the RegistryEnter a decimal value in MB. For example, 100 GB = 102400 Decimal (a GB to MB or bytes converter is below). Maximum Unicode pst/ost file size is 1TB or 1024 GB.

For ANSI format pst file, you need to create DWORD values named


Enter a decimal value in Bytes. For example, 1 GB = 1073741824 Decimal (a MB or bytes converter is below). Note that the maximum file size for ANSI pst is 1.9 GB.

Edit the registry

Administrators can control it using group policy by editing the following key.

As always, replace xx with your version of Outlook: 14 for Outlook 2010, 12 for Outlook 2007, or 11 for Outlook 2003.

MaxLargeFileSize – this value sets the maximum size of a Unicode pst or ost. In Outlook 2010 and Outlook 2013, the default is 50 GB; in Outlook 2003 and 2007, it’s 20 GB. Value range (in Hex) is 0x00000001 – 0x0000C800; when entering the value in Decimal, use MB.

WarnLargeFileSize – this value sets the warning level used with Unicode pst/ost files, so you know when the pst or ost is too large. The recommended warning is at 95% of the data file size. When entering the value in Decimal, use MB.

ANSI pst format

MaxFileSize – this value sets the maximum file size for ANSI format pst files. The default is 1.933 GB (2075149312 bytes), with the maximum allowed value of 1.9375 GB (2080392192 bytes). Value range (in Hex) is 0x001F4400 – 0x7C004400. When entering the value in Decimal, use bytes.

WarnFileSize – this value set the warning limit for ANSI format pst files. The default is to warn when the pst reaches 1.816 GB (1950368768 bytes) Value range is 0x00042400 – 0x7C004400. When entering the value in Decimal, use bytes.

Enter the values under the appropriate key for your version of Outlook:

Outlook 2013:

Outlook 2010:

Outlook 2007:

Outlook 2003:

Administrators will set these values using group policy:

Outlook 2013:

Outlook 2010:

Outlook 2007:

Outlook 2003:

Restore Default Values

To revert to the defaults, if the pst is larger than the default size, shrink the pst or ost so that its well below 20 GB (Outlook 2003/2007) or 50 GB (Outlook 2010/2013) or below 1.8 GB for ANSI format, then delete the appropriate MAX* and WARN* registry keys for the pst format.

Restart Outlook for the changes to take effect.

Do it for me

If you don’t want to edit the registry yourself, you can use the following .reg files to add the Unicode values to the registry.

Outlook 2013
30GB pst/ost – 29.5GB warning

Outlook 2010
30GB pst/ost – 29.5GB warning

Outlook 2007
50GB pst/ost – 95GB warning30GB pst/ost – 29.5GB warning

Outlook 2003
50GB pst/ost – 95GB warning30GB pst/ost – 29.5GB warning


  1. Paarass says

    I have problem that my mail box data file size limit is not increasing from 1.8 gb, whereas my need is atleat 20 gb.
    i have read the MSKB article 2months ago and do as directed but in vain, also read many other articles on online blogs (as above) but still my mailbox stop send/receive at 1.8GB. and I have to delete some email, that i wish to keep.
    I will be grateful if anyone help me.
    recently after reading this article, I have deleted the MaxFileSize and WarnFileSize and only keep the MaxLargeFileSize and WarnLargeFileSize with values set for 50GB. but still after restarting the MS Outlook, its stuck on 1.8 gb limit.

    Waiting for some help from you people. thanks, Paarass (

  2. George says

    I am using Outlook 2007. I have set up two emails/data files. The default is Exchange (ost), and the other is a Pop email account (pst). My pst email data keeps reverting to the ost default file without me doing anything, thus dumping all my personal emails into my exchange email inbox. Very annoying. any idea why this is happening?

    • Diane Poremsky says

      Go to Tools, account settings - select the POP account then Change Settings button at the bottom of the screen. Is the pst selected? Is the pst on your local drive? If the pst is not available, outlook will use the ost, which is available.

  3. Mark Pavey says

    Hi Diane - thanks for this very useful article. Unfortunately for me within the Registry Editor --> hkey_current_user --> software --> policies --> Microsoft i then only have 2 folders (SystemCertificates and Windows). There is no 'office' folder. Do you know why and what the fix is? Im on XP, and just installed MS Office 2010. Any help would be very greatly appreciated (i've got 180gb of email to transfer over from Outlook Express and it always crashes at 50GB due to this limit when i try to import!!).

    • Diane Poremsky says

      If the path does not exist, you need to create it. Or run the 100 GB key.

      Outlook doesn't create the default keys until you change them - but in the case of policies, they are not created until group policy is applied.

  4. Mark Pavey says

    Hi Diane - wow, thanks for very fast reply! Sorry i've never done any of this register editing before. If possible, could you tell me step-by-step how to run the '100 GB Key'? Do i need to install some program that handles the registry edits, such as 'Windows Registry Editor Version 5.00'? Basically, i have no idea where to put below!


  5. Mark Pavey says

    Sorry i've never done any of this register editing before. If possible, could you tell me step-by-step how to run the '100 GB Key'? Do i need to install some program that handles the registry edits, such as 'Windows Registry Editor Version 5.00'? Basically, i have no idea where to put that key. PS. sorry for posting this a 2nd time, just realized i did not 'reply' to your posting so perhaps you were not notified.

  6. Hector Frohm says

    Hello Diane,
    Thank you for your article. However, just like the other posts on limiting ost file size, it doesn't indicate what Outlook will do when the maximum file size is reached...
    When the PST size is not limited, but the OST file size is... What happens when the OST limit is reached ? I know Outlook will try to compact, but if the PST size is 20GB and the OST limit is set to 5GB.. will outlook decide to only cache the most recent 5GB worth of e-mails and make a call to the Exchange server if displaying an older e-mail is required ? Or will it just stop receiving new e-mails ?
    Thanks !!

    • Diane Poremsky says

      Outlook will stop receiving email if the ost is too large. If you use filters or Outlook 2013's Sync slider, the size applies only to the ost size, not the mailbox size, so mail arrives but won't sync to outlook. You should receive a notification that the ost is nearly full.

  7. Troy Gibson says

    i just changed the registry key under one of my users in the office. we are on a domain and have an in-house exchange server running exchange 2010 sp2. the user that i changed the registry key is using office 2010 and when i go to file on the top left corner, the data file size is still 20 gigs. is there a reason why this is happening? it seems the register edit isn't working. he used to use 2003 in the beginning and has upgrade to 2007 and then 2010..

    thanks in advance

  8. Timothy says


    I am using Office 2007 on a Windows 7 machine. I used your "do it for me" option to increase the file size to 100GB with a 95 GB warning. I am still getting the warning that my Outlook.pst has reached its maximum size. I checked the registry and the values have been set properly by your "do it for me" option. I have restarted my computer. Why am I still getting this warning?

    • Diane Poremsky says

      Thanks! The file size is 1.9 GB, that means its the old ANSI format. The file size key is for Unicode pst files. I would go to file, account Settings, Data file and click Add. Create a new data file and set it as default. Then either move calendar, contacts, tasks, and email to the new pst or close the old pst and import it into the new pst. (If you are using Rules, you may need to export them first).

  9. Timothy says

    I created a new pst file called Outlook 2007 so I remember this is the larger one. Your next instructions are beyond my limited skill set :( Which is the easiest ways to move the data into the new pst file? Is there a reference (step by step kind of thing) you could recommend that I could use as a guide to help me do this move? If not, would you be able to provide some more specific instructions on how to do this move? I don't know what I would do if I lost my email data!

  10. R. A. Mitchell says

    I was able to upgrade my Outlook 2003 to 100 GB using the "Do it for me" link, it even created a PST registry key where none existed before (this was on a Windows 7 laptop). I tried to do the same on my new Windows 8 machine (also a laptop) but I had to create a PST key before anything happened. My question is why did I have to create that key and did this mess up my registry? Your response will be greatly appreciated.

    • Diane Poremsky says

      The 'do it for me' file didn't do it? Are you using Outlook 2003 on the Win8 machine?

      BTW, no it won't mess up the registry.

  11. R.A. Mitchell says

    Thanks for your prompt response. Yes, I was using the same Outlook 2003 program on my Windows 8 machine, it's also good to know there shouldn't be any problem. The other Outlook registry key entries were a bit different on the Windows 8 machine when compared to my Windows 7 laptop, don't know what that's all about but the new machine's Outlook program is not yet set up to link with my online accounts.

  12. R. A. Mitchell says

    Thanks Diane;

    I'll keep looking into this and let you know if anything turns up. I doubt that it makes any difference, but both machines are ASUS brand notebook computers. I'll be linking the new machine to my online mail accounts soon and confirm that Outlook is behaving properly.

  13. George says

    I am trying to enlarge my maximum file size for my outlook ost file but my windows 8 registry doesn't have the key HKEY_CURRENT_USER\Software\Policies\Microsoft\Office\15.0\Outlook

    it only goes to HKEY_CURRENT_USER\Software\Policies\Microsoft

    surely there is some place that a max file size is kept, since outlook has told me I have exceeded it.

    • Diane Poremsky says

      If the key doesn't exist, you need to add it. (Outlook doesn't add keys to the registry for default values.)
      Administrator will use the Policies key, end users can use either policies or

  14. gcsimpson says

    I am using windows 8 and outlook 2013 installed from disk. All outlook activities are taking place in an OST account. Yesterday a popup said I had reached max file size. Tried to follow yours and microsoft's regedit suggestions,,, but I don't have the key


    only goes as high as


    and under that it only has SystemCertificates and Windows subkeys

    I suppose I could create the necessary subkeys but before I do, I'm wondering ...where is the registry key that is setting my current limit?

    • Diane Poremsky says

      If the key doesn't exist, you need to create it. Outlook only adds keys if you change the default value.

  15. gcsimpson says


    I assume there is a generic setting in the registry for maximum file size and then when I create the key, I am overriding it for outlook files? could you direct me to the location in the registry where the generic maximum file size is currently set. Sorry for being so curious, but I like to have some minimum understanding of what I am doing and how it all works together.

    • Diane Poremsky says

      The generic/default setting is baked in the outlook files, either in outlook.exe or one of the dll files. The reg key overrides the default.

      Pretty much all of outlook's default options are in the files, the reg keys are created only when you change the defaults.

  16. gcsimpson says

    I feel like a do-do, but you say the above instructions are for PST and OST; however, everything seems to deal with PST,

    "Browse to HKEY_CURRENT_USER\Software\Microsoft\Office\xx.0\Outlook\PST "

    I've even gone to the Microsoft site to save you the trouble of an answer but they have the same thing you have . . . only PST

    I could just use your macro, but I'm trying to learn, here. Do I change PST to OST or does PST set the values for both types of files.

    Ever thankful

  17. Fabio says

    Thank you very much for your help, I'm a computer technician and was looking for this solution for a long time, it really helped me a lot.

  18. Felix says

    Dear Diane,

    according to the Microsoft Knowledge Base the maximum valid setting for MaxLargeFileSize in Outlook 2010 and 2013 is 0x0000C800 - which translates to 51200 MBytes (50 GByte).

    However you offer .reg files that set this value to 100 GByte.

    Unless the information in the Microsoft Knowledge Base is wrong this setting should be ignored because it exceeds the Valid Data Range for MaxLargeFileSize.

    Can you (or maybe someone else) confirm that Outlook 2013 (or 2010) actually do support files significantly larger than 50 GByte?

    Kind Regards

    • Diane Poremsky says

      I will double-check. I asked about this KB before and was told it would be corrected. Its possible they decided the max should be 50gb because its less stable when larger, but it's more likely the kb is wrong. The default is 50GB and the max should be 1TB, but the optimal max size is 50GB.

      AS an FYI, the Office 2013 GPO has the max value at 4TB (4294967295 MB) for Outlook 2013.

    • Diane Poremsky says

      Ok.. due to a bug, 50GB is currently the supported maximum. (Outlook support followed up and said you can go higher than 50 but it's buggy.)

    • Diane Poremsky says

      Does the link not work for you or do you mean that you install the do it for me, but the pst or ost file size isn't increasing?

    • Don'twannacreateanaccount says

      That's because you probably have Outlook 2013, which is now on version 15. The reg editor file is still looking for version 14.
      Download the file, right click on it, Edit, and where it says "14.0" write "15.0" instead. Save it, close the notepad and run the reg editor file again. Registry should be updated in the right place now.

  19. ehansberry says

    Glad this site exists. I really think MS is wrong in their article at

    I tried that but you cannot even set a 50GB file size based on their instructions. It would be the number 53,687,091,200 (sans commas of course) which won't fit in a DWORD32 registry key. Their article makes it sound like you have to set the size in bytes, but Diane's reg file seems to have set it in MB, so 102,400 is 100GB.

    I am doing a large export from a business Gmail account that is over 50GB, so I'll know in a few hours if Diane's registry key worked. I have Outlook 2010 and did restart Outlook after importing the file.

  20. Aufinger says

    "it can be raised in Outlook 2003/2007" but what about 2010/2013? And why would one want to lower the 2010/2013 to 30GB?

    I have a 2013 user that has an Exchange mailbox slightly larger that 50GB and he wants to cache all of his data. What are the implications of raising the 2013 limit to say 75GB?

    • Diane PoremskyDiane Poremsky says

      You can raise it in any of the versions - it might be a little slower or less stable but should be ok. 50GB is what they feel is the maximum most stable size.

    • Aufinger says

      Do you have experience with raising the ost size limit in 2013? What kind of instability might one expect?

      Is the suggestion to lower the default included here because it might help in performance? I am still curious as to why one would want to lower the default.

    • Diane PoremskyDiane Poremsky says

      I've set the key in the pst but gave up trying to push it over 50 GB to test it. My current Exchange mailbox quota is 50GB and older messages are archived into an online archive so it never gets about 4 GB.

      The usual reasons for lowering the default is you have limited drive space and want to limit the pst size. Or the admin matches the max .ost size with the quota. Otherwise, there really isn't a reason to change it.

Leave a Reply

Please post long or more complicated questions at OutlookForums by

If the Post Comment button disappears, press your Tab key.