Learn How to Solve Outlook Oversized OST File Problem

admin | November 7th, 2016 | MS Exchange & Outlook

MS Outlook, one of the widely employed email application at an enterprise level saves its database in two file formats, i.e. OST and PST. Although they are like the fruits of the same tree, but their ways are separated by Exchange server. OST files come into existence, when Outlook is configured with Exchange server by enabling MAPI protocol. It would not be wrong to designate OST files as the replica of data residing on the Exchange server. An OST file acts as a depository, which stores entire mailbox data like emails, contacts, calendars, etc. OST files fulfill the desire of the users to work in offline mode either when the internet traffic is at peak or there exists Exchange server configuration issues. Both OST and PST file format has one similar feature that both has some file size limitation, which creates numerous of issues when its limit is exceeded. In the following section, we will discuss the issues and way to solve Outlook oversized OST File problem.

Problems behind Increased Size of Exchange OST File

Outlook has some predefined file size limitation of ANSI .ostdata file is 2 GB and for Unicode .ost file is 20 GB for Outlook 2007 whereas for Outlook 2010 & 2013 is 50 GB. However, when an .ost file increases this predefined file size limitation then, there are some performance issues, which are observed in Outlook. If it all these issues continue, it can lead to the corruption of OST file. When there is an increment in the number of mails then, some users might delete few of their OST mails in a manner to free up some space. If we see from the technical point of view then, it does not free the space of the .ost file from store locationas the deleted mails get saved in the Deleted Items folder and thus exist in the same OST file.

Due to oversized OST files, there are number of issues that are encountered by Outlook users as mentioned below:

  • Unable to load andopen data of .ost file.
  • Unable to add new data in the already existing Exchange .ost file.
  • Failure in synchronizing the offline OST file with Exchange server.

Difference between Mailbox and OST File Size

An increased OST file size does not always involve that the factor responsible for it is the increased mailbox size. Even though, the mailbox data does constitute the majority part in the OST file, there can also be additional data present in the OST file. In Outlook 2010 and previous versions, the size of OST file can be 20-30% larger than the mailbox size. This can be a result of storage deficiency or issue in calculating the mailbox size from Exchange part.

Way to Maintain Offline OST from Oversizing

In order to safeguard an OST data file from exceeding the defined file size limitation, users must keep in mind the mentioned points. It helps to optimize the file size of Offline Exchange Server OST file.

  • Delete all the undesirable .ost items from various folders of Offline OST file.
  • Hard deletion of items, which are not required. Moreover, keep the Deleted Items folder empty in a way to get permanently rid of the deleted messages.
  • Compress OST file size.

Methodology to Resolve Oversize Issue in OST File

All the above-discussed way can only work if user needs to protect their OST file from getting getting oversized. However, if the OST file has already crossed the file size limitation then, there are two ways to resolve it.

Remedial Methods

Some workarounds can be utilized to overcome from the oversize problem in OST file as mentioned. Before performing these methods, it is suggested to take the complete data backup.

  • Rename Offline OST File
    Many times, OST file may pose problems in execution normal operations in Outlook such as opening, sending, receiving, etc. This problem can be resolved by renaming OST file.  Just rename your OST file and restart Outlook then, utilize it.
  • Run Outlook In Safe Mode
    Running Outlook application in a safe mode may help to resolve the issues, which are faced by users due to Exchange .ost file.
  • Recreate Outlook Profile
    Since the user is using Outlook with Exchange server in a manner to work with OST files therefore, it is required to delete the current Outlook profile and create it again.
  • Disable All Add-Ons
    While using Outlook, there are some add-ons, which may be obstructing and disrupting its normal functioning. In such situation, it is superior to disable the add-ons installed in Outlook.
  • Archive OST File Data
    Archiving Offline Exchange Server OST file data in a new file may help in clearing the space, which is occupied on the server. This safeguard the data, which is stored on the server, from crossing the pre-defined size limit.  The archive file can be stored at desired location on the system.


All the above-mentioned methods do not properly work in all the cases. These are just hint and trial methods to resolve the problem.

Flawless Solution

If all the above mentioned methods do not work in your case or if you have already lost some data then it is better for you to repair the OST file items. To overcome from such a situation, there is a software namely OST Wizard that easily repairs the corrupted OST file and successfully convert OST to PST format. The application is algorithm in such a way that it makes easy for users to resolve corruption problem in OST file. The utility gives various inbuilt functionalities that manage and split the large size OST files in smaller parts.  The software is compatible with all the Outlook versions.

Noteworthy Features

  • Completely safe and secure to utilize
  • Supports all Windows editions
  • Retains the data integrity
  • No Exchange as well as Outlook connectivity required


While working if any hurdle in the workflow creates an issue in the workflow. Out of which, one such issue is oversize of OST file. In the above discussion, we have covered all the main reasons, which lead to oversize issue in Outlook OST files. Along with this, some methods are suggested that makes it easy to resolve such an issue. Expert 24×7 technical assistance is guaranteed for those who face any issue in resolving ‘How to Solve Outlook Oversized OST File Problem’ query.

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