Warning- Outlook OST has Reached Maximum Size in Outlook 2016 and 2010.

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  • Published on
    August 8th, 2019
  • Updated on
    February 24, 2021
  • Read Time
    4 minutes
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All the cached data of MS Outlook is stored in an OST file format on the local machine but sometimes due to the deficiency in storage space on the Outlook server, the OST files exceeds its size limit and the warning appears. Due to this problem the user frequently encounters Outlook OST has reached maximum size error. In this blog, I’ll discuss the various reasons why this warning appears and also cover all the techniques which would help you in resolving this warning.

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Factors Responsible for this Error

  • When an ANSI PST file exceeds the limit of 2 GB then the user faces this error.
  • Sometimes the Unicode PST file reaches its maximum limit of 50 GB then this warning appears.
  • Some registry policy might be conflicting OST file from increasing the size limit and leading to the warning.

Steps to Fix Outlook OST has Reached Maximum Size Error

Well, it is a quite lengthy process to fix this error and it includes three major steps. Let’s see how we can prevent this warning from occurring again and again.

Know Your OST File Type to Fix the Error

First of all, you must determine the type of file whether it is Unicode or ANSI.

  • Go to Start and then Open Control Panel.
  • Open Mails and Click on Data Files.
  • Open the OST file which is having the issue.
  • Click on the Advanced Tab and see the Message at the Bottom.
  • Mailbox Mode will tell whether the file is Unicode or ANSI.

Now, you have determined the type of OST file you are having. So if you are having ANSI OST file then create some space on it and reduce its size to less than 2 GB. Then these techniques will surely resolve OST has reached Maximum Size Error.

If you don’t want to delete items from the OST file then the only way left is to locate OST file and convert it ANSI OST to Unicode OST.

Locate OST File

  • If you are using Windows Vista or 7 then just follow the path given below:-


  • If you are using Windows 2000 or XP then follow another path given below:-

C:\Documents and Settings\-your-username-here\Local Settings\Application Data\Microsoft\Outlook\

Note-* You’ll find the OST file at the location only when the exchange server connected to MS Outlook.

Convert ANSI OST to Unicode PST

Once you have located the OST file now you should follow the steps given below to convert ANSI format to Unicode.

  • Disable the Cached Exchange Mode Settings.
  • Click on OST and Press F2 to rename the Extension from .ost to .old.
  • Now, Open MS Outlook and then Enable the Cached Exchange Mode Settings.
  • Close the Outlook application and go to the Location where OST files are saved.

I hope you have found a new database of OST file on the same location and now you can check the file, it would be surely a Unicode OST file.

Now, the maximum size limit of your cached data has been increased to 50 GB and you’ll not face Outlook OST has reached maximum size error. Here are Methods to Restore Data From An Orphaned OST File

Convert OST to PST

This is the most appropriate option for you that first, you should convert OST files to PST and then split it into several PST files. This will maintain all your data intact and prevent data loss. If you are thinking that you have to buy two separate tools for doing so then you are wrong because there is an option of OST Recovery Software.

  • Recovers Data from Large Inaccessible Files.
  • Converts OST files to PST.
  • Splits the Resultant PST Files into Multiple Files.

This software possesses the feature of three different tools into one tool. You can try this shortcut as well to fix the OST maximum size issue.


So the ball is totally in your court. I have given you three different solutions to deal with the issue. Creating space by deleting emails can resolve this error or increasing the capacity can prevent warnings. Last but not least, the OST Recovery Software which is the compilation of many features. So you can decide which method you want to opt and stop this error from occurring in the future.

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