Checking Outlook mailbox size frequently is important to maintain smooth performance and prevents from storage related issues. MS Outlook stores email, attachments, contacts, calendar, notes and other data, which gradually increases over time. As the mailbox grows, it starts to affect performance such as taking long time to load folders, syncing issues, application may become slow and show errors while sending or receiving emails.

Outlook uses two different formats to store data PST and OST, which depend on the account type. And these data files have size limitation, if recommended size exceed then your file may become damaged and unable to access data. Therefore, analyzing mailbox size helps to identify issues on time and manage inbox easily.

This write-up explains multiple ways to check Outlook mailbox size, understanding of PST and OST file size, and ways to manage large mailbox effectively.

Understanding OST and PST Files

Outlook stores mailbox information in two different formats PST and OST. File type depends on the email account configuration such as:

  • MS Outlook uses PST format to store POP3 accounts and archives locally.
  • An OST file is just a copy of your mailbox synchronized with the mail server. It creates automatically when Outlook connects with Exchange Server, Microsoft 365, Outlook.com, or IMAP accounts.

Modern version of Outlook from 2010 to 2021 and Microsoft 365 supports UNICODE PST and OST with a default maximum size of 50 GB. Once the mailbox approaches this limit, it starts affecting Outlook performance.

And this is the main reason to check Outlook mailbox size again and again on time.

Table of Contents
  1. Benefits of Analyzing Outlook Mailbox Size on Time
  2. How to Check Outlook Mailbox Size?
  3. What Happens If Outlook Mailbox Size Exceeds the Limit?
  4. Techniques to Fix Large Mailbox Issues
  5. Manage Large PST File
  6. What If PST or OST Severely Damaged due to Exceed Size?
  7. Conclusion

Benefits of Analyzing Outlook Mailbox Size on Time

Regularly viewing your storage limit helps to maintain smooth email communication and prevents errors. These are the key benefits:

  • It helps to reduce the lag, freezing and slow loading times.
  • Large mailbox size prevents you from sending and receiving emails.
  • Large Outlook data files are more prone to corruption and accessibility issues. It prevents your file from corruption.
  • Yes, smaller mailbox can sync faster with Exchange Server, IMAP, or Microsoft 365 accounts.
  • It helps to locate large folder which consuming excessive space, so you can clean them when required.
  • Also, checking your Outlook mailbox size improves productivity and keeps your email organized.

How to Check Outlook Mailbox Size?

There are multiple ways to view mailbox size in Outlook, depending on whether you want to check entire mailbox size, individual folders, or actual size of PST/OST files. Each technique is explained below:

Method 1: Using Mailbox Cleanup

  1. Open your Outlook.
  2. Head to the “File” >> “Info” tab.
  3. Choose the “Tools” >> “Mailbox Cleanup” option.
  4. After that, select “View Mailbox” Size.

Here you will see:

  • Total mailbox size.
  • Size of individual folders.
  • Local data size.
  • Server data size.

Method 2: Check Folder Sizes in Outlook

Mainly folders occupy the most space, so you can analyze them by following these steps:

  1. Right-click on the mailbox name from navigation pane.
  2. Select the “Data File Properties”.
  3. Hit on the “Folder Size”.

From here you can easily view:

  • Folder names.
  • Folder sizes in kilobytes.
  • Total mailbox size.

Users can easily analyze the folders containing large emails and attachments.

Method 3: Check PST and OST File Size

  1. Open your Outlook.
  2. Choose the “File” >> “Account Settings” >> “Account Settings”.
  3. Choose the “Data Files” tab.
  4. Select the PST or OST file and choose “Open File Location”.
  5. Right-click on your file and select the “Properties” option.

Default System Paths:

If your Outlook fails to specify the file location manually, then you can follow these paths via Windows File Explorer to check Outlook mailbox size:

PST – C:\Users\%username%\Documents\Outlook Files

OST – C:\Users\%username%\AppData\Local\Microsoft\Outlook

After finding the correct path, right-click on the target PST or OST file and choose Properties to see the file size.

What Happens If Outlook Mailbox Size Exceeds the Limit?

After checking Outlook mailbox size, you may find that your PST or OST file has already exceeded the recommended size limit. Oversized mailbox can affect performance and lead to several issues such as:

  • Slow Outlook startup and performance.
  • Outlook freezing or becoming unresponsive.
  • Errors while sending and receiving emails.
  • Delayed synchronization with Exchange Server, IMAP, or Microsoft 365 accounts.
  • Search functionality may stop working properly.
  • Mailbox quota warnings and storage notifications.
  • Increased risk of PST and OST file corruption.
  • Missing, duplicate, or inaccessible emails.

Fortunately, Outlook offers several ways to reduce Outlook mailbox size and improve performance. The mentioned techniques help you to free up space and manage large mailboxes efficiently.

Techniques to Fix Large Mailbox Issues

Outlook provides multiple built-in techniques to decrease the mailbox size. We have explained all methods one by one from simple to advance approach to fix all issues.

Delete Unnecessary Emails

Deleting old and unwanted emails is a simple step to reduce PST file size. If your mailbox containing unwanted old emails especially with large attachments then removing them permanently can fix issue.

Empty Trash and Spam Folder

After normal email deletion, data usually moves to Trash / Bin folder for 30 days. And Spam folder contains promotional emails. So empty both folders to make Outlook performance smooth.

Save Attachments Outside Outlook

Large attachments are the main cause of increasing Outlook mailbox size. So, you can save attachments locally for more storage space.

Archive Older Emails

Also, users can archive their old emails in separate PST file outside of Outlook by following steps:

  1. Head to the “File” >> “Info” tab in Outlook.
  2. Choose “Tools” >> “Clean Up Old Items” options.
  3. Select the “Archive this folder and all subfolders”.
  4. Now select the folder that contains older data to archive.
  5. Specify date range, and saving location.
  6. Hit the “OK” button to fix the issue.

Compact PST Files

After check Outlook mailbox size, Outlook provides offers built-in feature to compact large PST files and recover unused space.

  1. Open your Outlook.
  2. Head to the “File” tab.
  3. Choose “Account Settings” > “Account Settings”.
  4. Select the “Data Files” tab.
  5. Choose any PST file to compact.
  6. Select the “Settings” >> “Compact Now” option.
  7. Finally, wait for Outlook to reduce the file size.

Manage Large PST File

If nothing works for large mailbox, then you should download the SysTools PST Splitter Tool. This software allows to divide large files into smaller and manageable parts by size, folder, date, year, email ID, category, sender and subject.

You can split your file for better management. This software supports both ANSI and UNICODE PST files created by any Outlook version. For better analysis, use the free demo version.

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What If PST or OST Severely Damaged due to Exceed Size?

Yes, ignoring mailbox size limits for long period can cause your files to become damaged and corrupt. In some cases, Outlook can’t open data files, synchronize mailbox contents or access emails and attachments.

As manual techniques can’t recover data from corrupt PST and OST files, we should use automatic solutions to recover complete data without losing any information.

SysTools PST Recovery Tool helps to recover complete data into a healthy format for better management including emails, contacts, calendars, attachments, notes, journals etc.

And OST Recovery Tool by SysTools helps to repair and recover complete data including permanently deleted items into a healthy format. It works with orphan, inaccessible and damaged data files smoothly.

Conclusion

This blog has explained ways to check Outlook mailbox size, about OST and PST, benefits of analyzing mailbox on time, what happens if size exceeds, how it impacts and ways to resolve this issue. In case your Outlook mailbox is full, then follow the suggested techniques. For any queries, you can connect with us.