How to Reduce Large Outlook Mailbox Size in Outlook 2019, 2016, 2013?

Written By Ashwani Tiwari
Anuraag Singh
Approved By Anuraag Singh
Published On September 10th, 2022
Reading Time 7 Minutes Reading

It is very likely to have a large Outlook mailbox, since Microsoft Outlook is one such platform where technical as well as nontechnical users laboriously rely on to manage their data, in the form of Emails, Calendar Entries, Task management, note taking and much more. As this data goes into large amount, we need to reduce large Outlook mailbox size.

Being such a huge stand alone application, MS Outlook somehow has some limitations regarding storage and managing huge data. PST file is the database file where all this data is stored. And even though users have data in huge amount, PST file has its own size limit (20 GB for Outlook 2007 & 2003 and 50 GB for Outlook 2010 & above).

Moving to the methodologies on how to reduce size of Outlook mailbox, there are multiple manual, as well as automated techniques that we can use to reduce the size of Outlook and get rid of these large PST problems.

Why is The Overlarge PST File a Problem?

An Overlarge PST file is no good to users. It can harm both MS Outlook as well as user’s data. The enormous mailbox size can cause several problems like, Outlook crashing, hanging, freezing and even losing all the data.
Here is a listed description of all the harms that a large PST file can cause:

  1. PST File Corruption: PST file might get corrupted due to a large Outlook mailbox, which is not a good sign. The Outlook archive PST size must be reduced to avoid the corruption.
  2. Data Loss: The most disturbing outcome of an overlarge PST file is data loss. A corrupted PST file due to exceeded data is prone to damage data. In the worst case, user may lose their all data.
  3. Degraded Performance: Due to the over-large Outlook data file, Outlook becomes slower to respond, we might have to wait for a couple of minutes to open a single file, or in the worse condition, Outlook might get crashed.
  4. Less Productivity: A slower Outlook will definitely provide less output, which will ultimately make it less productive.

These all factors make the giant PST file a major problem.

How to Reduce Large Outlook Mailbox Size?

There are several methods to get the solution for how to reduce Outlook mailbox size. MS Outlook itself has provided a number of inbuilt methods to reduce the size of Outlook. Other than just selecting messages and deleting them one by one, we can use Mailbox Clean Up, Compact Now, Auto Compact, Archive Old Messages, Delete attached files and so on.

Let’s move forward to analyze all methodologies on how to reduce mailbox size in Outlook 2016 and other versions.

Method 1. Archive the Old Emails in Outlook

As the name suggests, you can archive your old Outlook mails by moving them from Outlook mailbox to archive file. Start with opening your MS Outlook.

  • Step 1. Visit File tab >> Info
  • Step 2. Click on Tools option >> Clean Up Old Items

Clean up Old Items

  • Step 3. A pop box “Archive” will show up, select Archive this folder and all subfolders option >> choose the file/folder to archive.

Archive this folder & Subfolders

  • Step 4. Check the option include items with “Do not Auto Archive” checked to archive the files that you do not want to include in automatic archiving.

Select Do not Archive option

  • Step 5. Hit OK

Method 2. Compact Now

This method is one power-pack and used most often by users to reduce size of Outlook mailbox. It a built-in utility in MS Outlook and also a powerful technique to reduce Outlook mailbox size.

How to reduce mailbox size in outlook 2016, 2013, 2010

  • Step 1. Go to the File tab.
  • Step 2. Next, Info >> Account Settings >> then Account Settings again

Account Settings

  • Step 3. Go to Data Files >> Settings >> choose the targeted file >> press Compact Now

Select Compact Now Option

  • Step 4. Click OK, exit.

How to Reduce Outlook Mailbox Size without Deleting in Outlook 2007, 2003?

  • Step 1. Visit File tab >> Data File Managment

Data File Management

  • Step 2. Double click on Data Files >> select targeted file >> Settings >> Compact Now

Select Compact Now

  • Step 3. Hit OK, exit.

Method 3. Mailbox Clean Up Tool

Try cleaning your heavy Outlook mailbox with Mailbox Clean Up utility.

  • Step 1. Click on File tab >> Info
  • Step 2. Choose Tools >> Mailbox Cleanup

Mailbox Cleanup

  • Step 3. Multiple options can be seen here like View Mailbox Size, Find items older than, Find items larger than, View Deleted Items Size, Empty Deleted Items, View Conflicts Size, and Empty Conflict

You can choose any of these options as you need.

Important Reminders
Keep in mind that manual solutions on how to reduce size of Outlook mailbox are a good way to go. But, its also important to know that these methods to reduce size of Outlook have some limitations as well.

  • Time Taking: Manual methods are indeed time taking. Even for a nontechnical user, it takes quite a lot of time to first understand the method and then apply it.
  • Data Risk: Any small mistake in between the steps of manual methods might lead users to lose their whole data. There are chances that user might get confused in between, which might be risky.

Method 4. Automated Solutions to Reduce Outlook Mailbox Size

There are two automated tools available that can help us to reduce Outlook mailbox size without deleting Outlook files i.e. PST Compress Tool and Split PST Tool. In the below section, we are going to discuss the process to reduce Outlook mailbox size in detail by using both tools one by one.

(1) SysTools PST Compress Tool – It is an expert solution to deal with extremely large PST files. The software covers all the areas where the above manual methods fail to work. Manual methods are the right choice when we have to reduce the size of Outlook mailbox in a really small amount. A very large PST file, say 1TB is hard to get compacted via all the manual methods. In such cases, it is advised to use this trustworthy tool to compact PST file. This software is designed with a user friendly interface that provides desired result in few simple steps, as follows:

Step 1 – Download and Run PST Compress Software.

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Step 2 –AddPST File or Folder to reduce the size of file.

Step 3- Select required Compression option: “Remove” or “Extract“.

Step 4 – Now, click “Next” button to start PST file compression and after the process down click on the OK button.

(2) SysTools Split PST Tool – If you are finding the proficient solution on how to reduce Outlook mailbox size without deleting Outlook files, Split PST Tool is the best way to do it. The software is built with breakthrough algorithms that make it highly capable to reduce Outlook mailbox of any size with in a really short time span. Also, the tool doesn’t modify or harm any of the user’s data. This PST Splitter tool is easy to use and works quickly in simple steps given below.

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Step 1 – Install and run Split PST Tool into the system.

Step 2 –Add” PST files / folder(s) and browse “Destination Path” to save resultant files.

Step 3 – Select desired “Split Option” (split by Size, Date, Year, Folder, Email ID & Category).

Step 4 – Check Summary of Split Information and click “Next” to proceed.

Step 5 – Now, PST splitting process has been completed.

Highlighted Features of Split PST Tool

  • Split Outlook PST file by Size, Folder, Date, Year, Email ID and Category
  • Allow to add single or multiple PST file/folder(s)
  • MS Outlook installation is not required while using Split PST Tool
  • Provide CSV of user’s email ID(s) to split PST by multiple emails
  • Break Outlook PST by size from 1 MB to 1 TB
  • Tool supports all editions of MS Outlook

Sum It Up

To reduce large Outlook mailbox size is not an exhausting task if done with the perfect planning and making the right choice. There have been instances where the huge Outlook mailbox is compressed down successfully with basic manual methods. On the other hand, the automated solution for how to reduce Outlook mailbox size is more secure and quick. It is also the best choice when we have to compress a very large Outlook data file.


By Ashwani Tiwari

Being a Chief Technical Analyst, I am aware of the technicalities faced by the user while working with multiple technologies. So, through my blogs and articles, I love to help all the users who face various challenges while dealing with technology.