outlook oversized ost file size problem

How to Fix Outlook Oversized OST File Problem?

OST file is one of the core file formats of Microsoft Outlook that let users work in offline mode. PST file format stores Outlook mailbox data and OST file comes into account when Outlook is used in cooperation with Exchange Server. Therefore, it is simply referred to as a replica of Exchange Server mailbox. No doubt every file format is different in their own but each of them has a predefined file format. Same is the case with the OST file, it also has some size limit depending on the version of Outlook. Sometimes the user has to face Outlook oversized OST file problem. So, when this size limit exceeds or a user has a large size OST file, it starts creating issues like performance degradation, corruption.  In most of the cases, users ignore that if OST file grows unnecessarily large, it will badly affect Outlook. Thus, it is always important to understand that keeping OST file in acceptable limit is really important. Now, the question of how to tackle these Outlook oversized OST file problem in a proper manner. In order to know about the same, continue reading the blog below.

The Outlook Data File has Reached The Maximum Size Issue -Know The Reasons

OST or Offline Storage Table has a predefined size limit i.e., ANSI OST file with 2 GB and UNICODE OST file with 20 GB & 50 GB. And, OST file stores all data that is created or received since the account is activated on Outlook. It contains emails, calendar, attachments, schedules, tasks, contacts, etc. Therefore, when a user forgets to delete unwanted data from the OST file, it becomes oversized. This will, later on, leads to corruption in OST file also and degrades the performance of Outlook. Most of the emails contain attachments in them due to which also OST file becomes large. In order to keep it in a healthy state, it is important to delete unwanted data.

List of Outlook Oversized OST File Problems

Whenever an OST file exceeds its file size limit, there are several issues faced by the users. All of them are discussed below:

  1. It becomes difficult for users to open or upload OST file data.
  2. A user is not allowed to add any more data in this Outlook oversized OST file.
  3. Microsoft Outlook starts hanging in between and creating an issue.
  4. Starts displaying error messages during a synchronization process.
  5. OST file is unable to synchronize with Exchange Server if it is unnecessarily large.

How to Prevent OST File from Growing Large?

Prevention is always better than cure. Therefore, protecting OST file from growing large, a user can refer the points mentioned below:

  • The very first thing that one can do is delete all unwanted items from all folders of OST file.
  • Shift + Delete the items that are no longer required. Moreover, clear the Deleted Items Folder and get rid of the already deleted messages permanently.
  • Compress Microsoft Outlook OST file.

How to Fix Outlook Oversized OST File Problem Manually

There is a possibility that the OST file has exceeded the predefined size limit. In such type of situation, a user can try some of the manual troubleshooting methods covered below:

    1. Rename Outlook OST File– It might be possible that OST file creates some issues while performing any operations in Microsoft Outlook. For example, send, receive open emails, etc. Thus, to overcome this issue renaming OST file is the only option. Now, simply rename OST file and restart Outlook and everything goes well.
    2. Start Outlook In Safe Mode – A user can also try to run Outlook in safe mode and fix common issues experienced by them because of OST file. There is a possibility that problems due to Outlook oversized OST problem file might get resolved because of oversized OST file.
    3. Create New Outlook Profile -In order to work with Outlook and Exchange Server, a user needs to take help of OST file. Therefore, a user can try to create a new Outlook profile and get rid of this error. This will help to resolve the increase OST file size Outlook Issue.
    4. Turn Off All Add-Ons– To make the task easy and more convenient for the users while working with Outlook, users install some add-ons. Therefore, it might be possible that these add-ons might disrupt the normal functioning of Outlook. Hence, to make sure this is the problem or not, try to disable add-ons installed in Outlook.
    5. Archiving OST File -Another possible way that a user can try is to archive the OST file data in a new file. This will surely help them in clearing some space on the server. This method will make sure that the server does not cross the predefined size limit. Apart from all this, a user can save this archived file at any desired location on the local machine.
    6. Turn Off Anti-Virus– The anti-virus and firewall available in the system can also create issues sometimes. So, disabling anti-virus for temporary basis can make lots of difference to Outlook performance.


This blog will let users understand about what all are the possible causes of large size OST file. In addition, there are multiple ways available that a user can apply to prevent OST file from becoming big. However, if a user is facing this Outlook oversized OST file problem, then he or she can try the various workarounds discussed above. If OST file gets corrupted due to the large size issue, then use OST to PST converter application and deals with any kind of OST file in a proper way.