Among many errors and issues of MS Outlook, OST reached maximum size error is a major one. This problem occurs when OST file of Outlook reaches its allocated file size. As the consequence, Outlook may start malfunctioning. To avoid such situations, it is necessary to know the solution to this issue. To educate users of the remedy of this problem, this write-up will share ways to fix Outlook reached maximum size problem. Before moving to the solution part, we will learn the causes of OST reached file size limit problem.

What Causes the Issue of OST Reached Maximum Limit

  1. Outlook File Size Limit: Outlook data file has got a fixed file size limit. When the file reaches that size limit or about to reach the limit, this error can occur. 
  2. Altered Registry Entry: Installation of two different versions of Outlook can lead to the change in Registry entry. In this situation, all entries do not get updated properly and causes this issue. 
  3. OST File Corruption: Sometimes, corrupt Outlook OST files can make this error appear. This problem is usually caused by Malware attacks. 

Solutions to Outlook Reached Maximum Size Problem 

There are several solutions to OST file size reached maximum limit problem. Here two of the solutions will be discussed. One of them is manual solution and another one is alternative method.

Let’s learn these two methods one by one.

Manual Method to Fix Oversized Outlook OST Problem

It is understandable from the earlier discussion that limited file size of Outlook is the main cause of this problem. Outlook 2002 or earlier versions of Outlook support ANSI type file that has maximum size limit of 2 GB. In modern time, 2 GB file size falls short against the requirement of the heavy users of Outlook. To avoid this situation, users can try changing their Outlook file type from ANSI to Unicode. Unicode is also Outlook file type but it supports up to 20Gb – 50 GB. Now, we will describe how to change ANSI file to Unicode and solve oversized OST problem.

Step 1: Find Out Outlook File Type

  1. Make sure that MS Outlook is closed completely. 
  2. Click on Start button on your Windows system and go to Control Panel. 
  3. Go to the Mail section and click Data File. 
  4. Double-click the Outlook data file that is having the problem. If MS Exchange appears, then the file must be OST. 
  5. Now, select the Advanced tab. 
  6. At the bottom, you will see that Mailbox Mode is being mentioned as Unicode or non-Unicode. 
  7. Make note of the file type. 

Step 2: Locate OST File in Your System

Go to Tools and then Folder Options>> View. Enable Show Hidden Files.

If you are using Windows XP, Go to this directory path:
C:Documents and SettingsUserLocal SettingsApplication DataMicrosoftOutlook

If you are using Windows Vista or Windows 7, go to this location:

Now, check the size of Outlook OST file. If the Outlook is connected to MS Exchange, there can be more that one OST file.

Step 3: Convert Outlook File Type to Unicode 

  1. Convert ANSI PST File to Unicode 
  2. Generate a new Outlook profile with an empty PST file. 
  3. If you are using Outlook 2003 or higher versions, the PST file will be created in Unicode format. 
  4. Now, transfer old PST files into the new one. 
  5. Convert ANSI OST File to Unicode 
  6. Make sure to disable “Cached-Exchange-Mode”. 
  7. Rename that particular OST file as outlook.old. 
  8. Open Outlook and shut it down. 

Try to re-enable “Cached-Exchange-Mode” now.
Outlook will now build OST file in Unicode format with Exchange Server data. This process may take some time to get completed. After completion, OST reached maximum size issue will get resolved.

Limitations of Manual Method
There are certain shortcomings of this manual method. This method can be used only if the Outlook file type is ANSI. If this problem appears in Unicode Outlook, then this method will prove to be completely ineffective. Many people do not find this method effective to resolve this problem.

Solution 2: All-In-One Solution to Resolve OST Reached Maximum Size 

As manual method cannot resolve this issue for all Outlook users, people tend to look for alternate method. Using third-party tools like OST Recovery has proven to be an all-in-one solution to this error. Difference in Outlook file type does not matter here as this tool is capable of solving this error. It will allow you to convert OST to PST format and divides PST file into smaller parts and thus increases the overall capacity of OST files. This application can process any size of Outlook files, so large OST file owners have no reason to worry. Even novice users can operate this software without any trouble. 
OST reached maximum size is a problem that can affect any Outlook users. Though it is mostly prevalent among users of ANSI Outlook file users, Unicode Outlook users can also face this problem. This post shared ways to get rid of this problem and users can choose from the methods mentioned. However, it is better to choose the all-in-one solution to avoid the limitations caused by manual method. This application splits OST file into smaller parts and solves the problem of OST files reached file size limit.
Previous articleView & Convert PST to PDF Adobe Acrobat Without Outlook – Tips & Tricks
Next articleLotus Notes Read Emails Showing as Unread
Diptesh Kumar Bhakat is proud to be the author of fastest growing tech blogs. He is a tech-savvy, SEO Expert, SMO Expert, SMM Specialist and a professional Blogger. Except blogging, he is so much found in photography, superbike riding. He has a very close attachment to the tech world and loves to blog on his fav topics. He has also contributed to many regional dailies and authored guest posts on some of the leading tech blogs. Professionally, he is a tech blogger and reviewer. he is a very energetic person who constantly puts up an evil smile to counter any obstacle in his manner. This dude is highly unpredictable and in reality, you can’t recognize what’s coming from him…be it his articles, generating an aura, or his personality. Mr. Diptesh is completed his B.Tech in Mechanical Engineering, as everybody thinks about one question that how a mechanical engineer can make a website?? Is it strange!!!!!!!! Yes it is. But there is a big story we will update soon.


Please enter your comment!
Please enter your name here