Outlook error "0x8004060C" occurs when the data file (PST or OST) reaches its maximum size limit, which prevents further emails from being sent or received. For example, in Outlook 2007, the maximum PST file size is 20GB.


You will receive a notification error message when ongoing send/receive action like “Task 'example@server.com – Receiving' reported error (0x8004060C): 'The message store has reached its maximum size. To reduce the amount of data in this message store, select some items that you no longer need, and permanently (SHIFT + DEL) delete them.'”



IMPACT OF ERROR

  • Won't be able to send/receive new emails until the file size is reduced.




RESOLUTION STEPS:

  1. Identifying Large items: Look for emails with large attachments and no longer be needed.

  2. Permanently Delete Items: Select and delete unwanted emails or attachments by using SHIFT + DEL to permanently remove the item.



Increase Size Of Outlook’s Store Maximum PST File Size Limit:

Warning:

Before modifying the Windows Registry, it's recommended to back it up. Incorrect changes to the registry can cause system instability.


Step To Increase Outlook PST File Limit


1: Backup the Registry (Optional but Recommended):

  • Press Windows Key + R to open the Run dialog.

  • Type regedit and press Enter.

  • In the Registry Editor, click File > Export, name the backup file, and save it.

* Make sure Outlook is closed when modifying the registry!

2. Open the Registry Editor:

  • Press Windows Key + R, type regedit, and press Enter.

3. Navigate to the following location depending on your Outlook version:

  • Outlook 2003:
    HKEY_CURRENT_USER\Software\Microsoft\Office\11.0\Outlook\PST

  • Outlook 2007:
    HKEY_CURRENT_USER\Software\Microsoft\Office\12.0\Outlook\PST

  • Outlook 2010:
    HKEY_CURRENT_USER\Software\Microsoft\Office\14.0\Outlook\PST

  • Outlook 2013:
    HKEY_CURRENT_USER\Software\Microsoft\Office\15.0\Outlook\PST

  • Outlook 2016, 2019 & 365 : HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Outlook\PST

For Domain Administrators: (Group Policy)

  • Outlook 2003: HKEY_CURRENT_USER\Software\Policies\Microsoft\Office\11.0\Outlook\PST

  • Outlook 2007: HKEY_CURRENT_USER\Software\Policies\Microsoft\Office\12.0\Outlook\PST

  • Outlook 2010: HKEY_CURRENT_USER\Software\Policies\Microsoft\Office\14.0\Outlook\PST

  • Outlook 2013: HKEY_CURRENT_USER\Software\Policies\Microsoft\Office\15.0\Outlook\PST

  • Outlook 2016, 2019 & 365: HKEY_CURRENT_USER\Software\Policies\Microsoft\Office\16.0\Outlook\PST

4. Create Or Modify Necessary Registry Values:

  • Create PST File:

  1. If there is no “PST” file, right click on the Outlook and SELECT New > Key and name it “PST”

  2. In the PST folder, you need to create or modify the following two DWORD (32-bit) values:

  • MaxLargeFileSize: Defines the maximum size of a Unicode PST/OST file in megabytes (MB).

    • Right-click in the right pane and select New > DWORD (32-bit) Value.

    • Name it MaxLargeFileSize.

    • Double-click it, select Decimal, and enter a value in MB (e.g., enter 30720 for 30GB).

    • Press “OK”

  • WarnLargeFileSize: Defines the warning threshold in megabytes (MB) when you’re nearing the file size limit.

    • Right-click and select New > DWORD (32-bit) Value.

    • Name it WarnLargeFileSize.

    • Double-click it, select Decimal, and enter a value slightly lower than the max size (e.g., 29000 for a warning at 29GB). 

    • Press “OK”

* Almost take 95% size of MaxLargeFileSize

**NOTE:

Starting from Outlook 2010, the default size limit for PST (Personal Storage Table) and OST (Offline Storage Table) files was increased to 50GB. This default size limit is the same for Outlook 2013, 2016, 2019, and Office 365 versions. 

  • Outlook 2003 & 2007:
    Default size limit is     20GB for Unicode PST/OST files.

  • Outlook 2010 and later (including 2013, 2016, 2019, and Office 365):
    Default size limit is     50GB for PST/OST files.

Example Values:

MaxLargeFileSize:

  • 20GB = 20480 (in MB)

  • 30GB = 30720 (in MB)

  • 50GB = 51200 (in MB)

WarnLargeFileSize:

  • 19GB = 19456 (in MB)

  • 29GB = 29696 (in MB)

  • 48GB = 49152 (in MB)

  1. Close Registry Editor

  2. Restart Computer or Outlook for the changes to take effect.

________________________________________________________________________

Note:

For optimal performance, it’s recommended to set the WarnLargeFileSize slightly below the MaxLargeFileSize to avoid sudden crashes when nearing the limit.

This method works for Outlook 2003, 2007, 2010, and 2013 to extend the maximum size of your PST or OST file.