How to Fix Mailbox Size Exceeded Error 0x8404060C?


In Microsoft Outlook, you may receive the error 0x8404060c, while sending or receiving a new message or email. It may also appear when you try to sync a large or oversized OST file.

The error message reads as follows:

“Task …..-Sending’ reported error (0x8404060c): 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.”

As a result, you can neither send nor receive emails in your Outlook client. This also prevents you from syncing your local mailbox to the server and vice-versa. Also, the error is not version specific. It may appear in Outlook 2007, 2010, 2013, 2016, 2019, and 2021.

In this post, you’ll learn the reasons that may cause the error 0x8404060c and the solutions to fix this error.

Reasons for Mailbox Size Exceed Error 0x8404060c

The Outlook error 0x8404060c is usually occurred when the size of the local cache or Outlook data file (.OST) that stores all mail items on your local storage reaches or exceeds the default mailbox quota. The error may also occur when the OST file becomes inconsistent due to oversizing, thus preventing Outlook from storing or writing new data. Below are a few more reasons that can directly or indirectly lead to the error 0x8404060c:

  • Low storage on the drive where OST is stored
  • Abrupt shutdown or power failure
  • System crash
  • Incompatible add-ins
  • Corrupt Outlook profile
  • Excess mail items per folder

Solutions to Fix Microsoft Outlook Error 0X8404060c

Below are some solutions that you may follow to troubleshoot and resolve the 0X8404060c Outlook send/receive error.

Clean Up Deleted/Junk/Spam Mail Folders

To resolve the error 0x8404060C, you can reduce the OST file size by cleaning up your mail folders, such as the Deleted Items folder and other mail folders. The steps are as follows:

  • Open Outlookand go to File > Tools or File > Cleanup Tools.
  • Select the Empty Deleted Items Folder

Empty Deleted Items Folder

  • In the new dialog box that opens, click Yes to confirm.

If you often delete emails, you can automate this process in Outlook by enabling the option to automatically empty the Deleted Items folder as soon as you close the application. This can help prevent OST file size inflation.

Follow these steps to enable this option:

  • In Outlook, navigate to File > Options > Advanced.
  • Under the Outlook start and exit section, click the Empty Deleted Items folders when exiting the Outlook 

Empty Deleted Items folders when exiting the Outlook

  • Click OK to save the changes and restart Outlook for the changes to take effect.

From now onwards, the Deleted Items folder will be emptied automatically as soon as you exit or close the Outlook client.

Note: All accidentally deleted emails will also be purged if you enable this option.

For Junk/Spam mail folders, you will have to manually purge them regularly to avoid exceeding the mailbox size. You can use the sort option in Outlook emails to list emails based on their size (from largest to smallest). From the list, select the emails you no longer need and delete them. Now, try to send or receive emails and see if the 0x8404060c error is resolved.

Clean up your Mailbox

Outlook provides an option to clean up mailboxes to reduce mailbox size (OST). Follow these steps to clean up your mailbox:

  • Open Outlook and go to File > Info.
  • Choose the Tools Cleanup Toolsor Cleanup Tools option and select Mailbox Cleanup.


  • In the Mailbox Cleanup window, select the appropriate value in the Find items larger than field and click
  • Clean up the mailbox.

Turn Off Cached Exchange Mode

Switching off or disabling Cached Exchange Mode switches Outlook to online mode. In Online Mode, Outlook connects to your mailbox server and changes are updated in real-time between Outlook and the server. Thus, there isn’t any synchronization. Although this will fix the error, you cannot access or use your Outlook when the system isn’t connected to the internet.

To turn off the Cached Exchange mode, follow these steps:

  • Open Outlook and go to File > Info > Account Settings > Account Settings.
  • Choose the email account and click Change.
  • Uncheck the Cached Exchange Mode option and click Next.
  • Confirm when the prompt appears and restart Outlook for the changes to take effect.

You can now send and receive emails without encountering the Outlook error code 0x8404060c.

Archive Unwanted Emails

Archiving old mail items not only helps reduce the size of your Outlook data file (OST) but also preserves your old mail items in a local archive (pst) file. Thus, you can always have access to the mail items without inflating the OST.

To archive your local mailbox, follow these steps:

  • Open 
  • Navigate to File > Info > Cleanup Tools > Archiveor File > Info > Tools > Clean up old items.
  • Choose the Archive this folder and all subfolders option and choose the mail folders from where you want to archive emails, usually Inbox and Sent Items.
  • Choose a date in the Archive items older than and then click Browse to choose a save location.

 Archive items older than

  • Click OK. This will move all emails older than the selected date to a local archive at the selected location in the .pst file.

Remove White Space from OST

You must remove white space from the OST file after deleting emails, archiving mail items, or cleaning up the mailbox to effectively reduce the file size.

To compact and remove white space from Outlook OST data file, follow these steps:

  • Open Outlook and navigate to File > Account Settings > Account Settings.
  • Click Data Files and select the Outlook OST file from the list.
  • Click the Outlook Data File Settings. button.

Outlook Data File Settings

  • Click the Compact Now This will compact the OST file and remove white space, thereby reducing the overall OST file size.

Once done, try sending an email and check if the error 0x8404060c persists.

Note: Compact option is available in Outlook 2010 and later versions and works when OST has more than 20% of ‘white space' (unused space).

Recreate OST File

When OST file is inconsistent or has partial damage, it may allow access to mail items but also lead to synchronization issues leading to errors, such as 0x8404060c. However, you can recreate the OST file to fix the error. The steps to recreate the OST file are as follows:

  • Close Outlook and find OST at the default location. You can go to File > Account Settings > Account Settings > Data Files to view the path.

Account Settings

  • Open the location, create a backup of the OST, and delete the OST file.

Once you have deleted the OST file from your system, start Outlook. Outlook will look for the OST file. Since you have deleted it, Outlook will create a new OST file and start synchronizing the mail items from the server. This will take a while to complete.

Once done, check all your emails and ensure all emails are synced. If you find missing mail items, you can restore them from the old OST file by using an OST to PST converter tool, such as Stellar Converter for OST.

The software can extract mail items from inaccessible, orphaned, or encrypted OST file and save them in Outlook importable PST format with complete integrity. You may also export the mail items from the OST directly to an existing Outlook profile, Office 365, or live Exchange mailbox.


Keeping the mailbox size under the limits and preventing it from reaching the maximum limit is critical to prevent synchronization errors and send/receive issues, such as error code 0x8404060c. These errors can prevent you from sending or receiving new emails or accessing your email account in Outlook. In this article, we shared the solutions to troubleshoot and fix the Outlook mailbox size exceeding error 0x8404060c.

You can use the OST to PST converter software, such as Stellar Converter for OST, to restore the missing mail items after fixing the problem by creating a new profile or recreating the OST file. You can also use the software to export the mail items from the OST file when it becomes inaccessible or orphaned (when the profile is deleted from the mailbox server) to PST format.

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