Reduce Outlook Mailbox size by Manual Method

Updated on December 02, 2022 by Savita Sharma

Microsoft Outlook is one of the best and most used email clients, as well as Office 365, Windows Live Mail and others. But just like the other email clients, users also face some problems while using it.

Do you ever get a notification from Outlook that says your mailbox is full of messages and you need to reduce your mailbox size for further use? For some reason, there might be a lot of unwanted emails and attachments in your mailbox that you haven't cleared out for the time being, which is why your mailbox now has no space.

But before starting the mailbox reducing process, you need to take a backup of the Outlook PST files. You can easily do it by using the Regain Outlook PST Recovery software.

What Kind of Issues Happen Due to Excessive Mailbox Size in Outlook?

Generally, Outlook users receive the mentioned errors because of the increasing mailbox size in Outlook. If you have got this error, it means your Outlook mailbox is completely full and there is a chance that you could face issues as follows:

  • Slow performance and low productivity.
  • It can happen that you will be unable to send or receive any kind of email.
  • For oversize, there is a chance that the Outlook PST file can be corrupted.
  • If the corruption of PST files increases due to oversize, there is a risk of data loss, and Outlook will throw an error every time, disrupting your work.

How to Reduce Outlook Mailbox Size in an Easy Way?

As you have read above, it's common to have the above errors if your mailbox is full. The majority of the time, you will receive send and receive errors, such as being unable to receive emails because there is insufficient space in your Outlook mailbox to add more emails.

Deleting some emails is the first aid to curing this issue. But the reasons for this situation can be different depending on many materials. In this post, you will get knowledge about multiple methods to deal with this full mailbox error. Keep reading and applying.

Remove the large emails with attachments.

I think there is no other easy way to delete extra-large emails that have bigger attachments. But deleting emails manually one by one is too disgusting, isn't it? However, you can perform the deleting process with an in-built facility in Outlook. Read as follows:

  • 1. Firstly, run Outlook and in the folder list, press on the search folder option. Then choose a new search folder.
  • How to Reduce Outlook Mailbox size
  • 2. Next, scroll down your mouse's wheel and under the section of "organizing mail," choose "large mail" and just press "choose.
  • Manual Tips to Reduce Outlook PST file size
  • 3. After that, provide a specific size in the box named "show mail greater than" and just press the OK option to begin the process.
  • Remove large attachments to reduce Outlook Mailbox size
  • 4. Press the OK button again and a folder will be created with your given specific size. Here you will find all the emails and attachments of that size that you have selected previously.

You can delete the folder to get some more space. However, you can also create a specific folder previously, and whenever you get the error of low space in your Outlook mailbox, you can easily delete the folder and get the additional fixes.

Archive or delete the old PST files.

There is an in-built facility in Outlook that can archive your old and unwanted.pst files into a different PST file on your device's local drive. Now, attempt the steps as follows:

  • 1. Firstly, run MS Outlook and navigate to Files > Options and then "advanced".
  • 2. Then go to the "auto archive" section on the menu and press on the "auto archive settings".
  • 3. Next, mark the checkbook "Run AutoArchieve." (you can select the desired number of days).
  • 4. Input other options like deleting old items or others, and lastly, just press "auto archive".

Use the built-in mailbox cleanup tool.

Usually, there is an in-built feature of Outlook through which you can reduce the size of your Outlook mailbox. Follow the below steps and procedures to get access to the Outlook mailbox cleanup tool and reduce the Outlook mailbox size.

  • 1. After opening Outlook, go to the "file" tab. From there, go to the "info" section and select the "Mailbox Cleanup" tool.
  • Free Manual ways to Compact PST file size
  • 2. If you double click on the mailbox cleanup, you will get three options under it as a drop-down list. They are as follows:

    • Mailbox Cleanup
    • Empty
    • Archive
  • 3. The first option, "Mailbox Cleanup," is generally used to see your mailbox size and find the folder with your given specific size.
  • Reduce or compact PST file size manually
  • 4. It also has the facility to archive items. By just pressing on the "AutoArchive", you can easily archive the unwanted items and move them to your desired location.
  • step by step process to compress Outlook mailbox size
  • 5. Using the "Empty" option, you can easily delete (permanently) all the items from the deleted items folder. You have the opportunity to view the folder.

Split or Divide the large PST files.

In Outlook, data files are usually stored in PST formatted files. Some PST files are so large that they take up a huge space in the mailbox. Don't worry, you can compress or split them to reduce the size of the mailbox. You can do it manually or through automated software.

For the manual method, you need to delete the unwanted files first. Go to the navigation panel, right click on the deleted items folder, and lastly press on "Empty". After that, follow the steps outlined below.

  • Run Outlook and in the "file" tab, press on the "account settings".
  • Navigate to the "Data Files" tab, then choose the PST files to compress and press on the "settings".
  • Lastly, in the "Data File" dialogue box, just press on the "Compact Now" option.

Besides, you can use automated software. You can easily split or divide the large-sized PST files into small sizes by using the "Regain PST Splitter" software. The most extensive facility which you will love is its easy and stunning interface.

How to split Outlook PST files using the Regain PST Splitter?

It's so simple to reduce Outlook Mailbox file size using this software. The steps are as follows:

  • 1. Firstly, install the software and run it on your device.
  • 2. Then choose the files that you want to split.
  • 3. After selecting your desired files, just click on the next button.
  • 4. Provide a location where you need to save the files.
  • 5. Lastly, after completing the splitting process, files will be saved at your given location.

Regain PST Split Software - Features:

  • Offers various PST file splitting options such as Split by Size, Split by Date, Split by Year, Split by Email ID, Split by Contain Words, To, From, Cc, Bcc and Subject.
  • Supports splitting corrupt, damaged, or inaccessible, password-protected Outlook PST file, and Outlook PST Archive files by date, size, year, or folder.
  • Maintains the emails integrity, email properties, folder structure, integrity, and hierarchy of Outlook PST files.
  • Splits large or oversized Microsoft Outlook PST file into smaller PST files and creates a Log Report to compare PST file on Split PST file process completion and saves in CSV format.
  • Splits large-sized Outlook PST file without Outlook installation and supports searching Outlook PST file from Drive.
  • Allows splitting Outlook contacts and calendar items apart from email items and makes new folder to save the newly-created PST files.


This article discusses the various issues that could happen due to increased Outlook mailbox size and the different manual methods for reducing Outlook mailbox size. We recommend using an advanced and professional Regain Outlook PST Splitter tool to split large-sized or oversized Outlook PST files into smaller PST files and thus helps prevent PST files getting corrupted due to oversize. This third-party tool is also available as a free Demo version to let users check its capabilities before deciding to purchase the full licensed version.