Come Comprimere File OST Grande ?

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You may be wondering why your computer is limping to Compress Large OST Files while it can smoothly run a 100GB game in Full HD resolution. It is because a large OST file or a large OST file may require a lot of bandwidth to synchronize with the server containing the OST file, Errors have been detected in the PST file.

So, if you have faced an error related to Compress Large OST File, in this article, you will get to know all the reasons behind “OST file too large” and possible manual and automated methods to resolve this issue

Why is My OST File So Big?

OST file stores all the Outlook data that is accumulated from the point you created your account. Additionally, it also stores all the emails, attachments, contacts, tasks, notes, etc. Generally, it might not sound like a lot but, in the long run, slowly and steadily, the OST file grows size.

If you forget to delete the unnecessary items, slowly they pile up and exceed the Outlook ost file size limit. This results in OST file corruption and problems while using Outlook.

Why are Large OST Files such a Big Problem?

First, an OST or offline storage table file works on the principle of synchronization. This means that you can work on Outlook even when you are offline and later synchronize with the server when the Internet connection is available.

Since the functioning of an OST file depends entirely on synchronization, the larger the OST file, the longer it takes to synchronize with the online server and results in  Outlook sync errors .

It doesn't stop there, Outlook continues to perform regular data integrity checks, so again, the more time it takes to check the OST, sometimes it may get stuck in integrity checking otherwise known as  integrity checking Outlook data locked error . This is why a large OST file that seems small can become very complicated to manage.

A large OST file can lead to the following problems:

  • Unable to access .ost file document.
  • Unable to add data to existing Exchange .ost file.
  • MS Outlook program crashes or crashes
  • Error messages during the synchronization process

How Big Can an OST File Be?

Version OST file size limit
Outlook 2007, 2003 20 GB
Outlook 2010, 2013, 2016 50GB

Note:  Whenever you fix an error, a smart step you can take is to archive the contents of the OST file. Because, when you are working to fix any Outlook related errors, you may damage your OST file. The instant and easy way to backup OST file is by using  Remo Outlook backup and migration , a one-stop tool for all Outlook related issues. With the help of Remo, you can backup, restore and even migrate your OST file.

Luckily, there is no need to stress over how to fix oversized OST file, Outlook has a built-in utility that will help you reduce the size of OST file, known as “ compact now ” option.

How to Compress Large OST File?

Luckily, there is no need to stress over how to fix oversized OST file, as Outlook already has a built-in utility that will help you reduce the size of OST file, known as “compact now” option. You can easily compress .ost file in Outlook to shrink Outlook ost file. Follow the below-mentioned steps to compress large OST file:

Step 1:  Go to the File  tab.

Step 2:  Then click on Account Settings .

Step 3:  Select Data File  option.

reduce .ost file size

Step 4:  Double click on D ata File  option which opens Outlook Data file settings  dialog box with Compact Now option.

Step 5:  Click compact now  to reduce the size of the OST file.

Program to Compress Large OST Files

Mailbox is larger than OST files due to inconsistencies in calculation. In Outlook 2007 and earlier versions of Outlook there were inconsistencies in size calculations and file structure that made the mailbox 20% to 30% larger than the corresponding OST files. In case of Outlook versions prior to 2010, the Outlook size calculation is more taken into account. The latest Outlook uses compression technology that automatically compresses text. Which again made the OST file smaller than the corresponding mailbox.

How Can I Fix OST Has Reached Maximum Size?

Looking for ways to compress .ost file in Outlook or reduce .ost file size .oversize. You can follow the below mentioned information to reduce the size of the .ost file which has reached the maximum limit.

Additional Information : If you are facing an error in Outlook that says “The Outlook data file has reached its maximum size”. It is due to a large PST file, know how to deal with a  large PST file has reached maximum size .

  • Using cleanup option to reduce OST file size

Outlook also has an option that will allow you to clean all unnecessary files from the trash with just one click. Since, OST file also stores deleted items, by not cleaning the deleted items accumulate and result in a large OST file. To archive the file follow the steps given below:

Step 1: Open Outlook and Go to File tab.

Step 2: Click on the  Tools option and then select Mailbox Cleanup

Step3: Then select the Empty deleted items  folder to erase all deleted items with just one click.

  • Alternative method to avoid oversized OST files

Step 1 : Open Outlook and click on Tools option.

Step 2 : Then click on Mailbox Cleanup Wizard which is a dedicated wizard that has all the options that will help you manage redundant data existing in your mailbox.

Step 3 : In the Mailbox Cleanup dialog box, click on “View Mailbox Size” option to view the mailbox size i.e. the size of the local OST and the size of the mailbox on the server

Step 4 : Now to compress large OST file, choose one of the provided options,

  • Find items older than: To find and delete emails older than a certain number of days that you no longer need.
  • Find items larger than: To find and delete emails that are larger than a certain size.

In case you want to reduce the size of OST file without deleting previous emails, follow the next method.

  • Disable all enabled add-ons

There may be a possibility that the add-ons interrupt the normal working of MS Outlook. So, disabling them wouldn't be a bad idea. Follow the steps below to disable add-ons and fix ost file issue efficiently.

Step 1 : Open Outlook. Go to the File menu. From the options, click Add-ins .

Step 2 : In the Manage Add-ins option which is at the bottom, select the COM Add-ins and hit Go .

Step 3 : Uncheck the Add-ins that are not in use and click OK .

However, these are temporary solutions and cannot guarantee that the OST oversized error will not recur. Fortunately, there are some changes you can implement on Outlook that will avoid the oversized OST problem.

  • Use AutoArchive to reduce OST file size

AutoArchive is a comprehensive tool that can be really useful for extended Outlook users. It will make regular archiving easier without any intervention. Below are instructions on how to use AutoArchive to avoid oversized .ost files:

Step  1: Go to  the Cleanup option.

Step  2: Click on the Cleanup option and then select  Mailbox clean up 

reduce .ost file size

Step  3: You will have an  AutoArchive option . Select this option to move older items in your mailbox to the archive folder.

Does archiving reduce the size of the OST?

Yes, regularly archiving your OST or Outlook data file will create a backup which relatively reduces the size of the OST file on the server. Which will also adjust the OST file size from reaching the limit. You can archive the file using the Clean option to avoid oversized .ost files.

Move mail items from OST to PST or archive folder

You can compress the size of OST file and also keep backup of previous emails by exporting emails to a local PST file. This method will significantly reduce the size of the OST without deleting any Outlook data, Outlook Profile to New Computer.

  • In Outlook 2013,
    • Navigare verso File > Cleanup Tools > Archive 

reduce .ost file size

  • Nel Outlook 2016 or 2019,
    • Navigare verso File > Info > Tools > Clean up old items

reduce .ost file size

  • Then select the ' Archive this folder and all subfolders ' option
  • Choose an email folder from the list for Archive
  • Then choose the date in the ' Archive items older than: ' option
  • Click Browse to select a save location and then click OK.

It will create a PST file in the selected location and a folder in your Outlook profile. However, the data stored in this folder is stored locally and not synchronized with your inbox.

The fixes for Outlook ost file has reached size limit mentioned in this article will help you reduce the size of your OST file or free up server space. However, a large OST file generally leads to corruption of data files. And if this is the scenario, your Outlook data could be at risk. To safeguard your data from loss, you will need a professional tool to overcome the issue of large OST file causing inaccessibility issues in Outlook.

Remo Outlook OST to PST Converter can safely convert any corrupt, damaged, orphaned or inaccessible OST file to PST. This tool will recover all your Outlook data including emails, contacts, calendars, notes and other Outlook items. Best of all, it retains the original OST file's folder structure, rules, autofill text, etc. Transfer OST file to New Computer.


The above-mentioned are some methods that can help you deal with a large .ost file. This article will be further updated as we come across new updates regarding the compact Outlook .ost file. Suppose if you are facing any issues not mentioned above, please let us know in the comments section below and let us know if this article helped you.

About the Author: Remo Software