Outlook Fix - Classic Outlook (Windows)
Fix Outlook error 0x8004060c (mailbox full)
Error 0x8004060c means "the message store has reached its maximum size" - your Outlook data file (the PST or OST that holds your mail) is full, or it has become corrupt. Send/Receive stops and new email will not arrive. The fix is to free up genuine space, then compact the file so Outlook reclaims it, and repair the file if needed. Here is the safe, step-by-step way to do it on classic Outlook for Windows, or we will sort it remotely in minutes. Rated 4.9 on Google.
- ● Empty Deleted & Junk
- ● Compact Now
- ● scanpst repair
What it means
What error 0x8004060c means
Outlook keeps your mail in a data file on your PC - a .pst for POP/IMAP accounts or an .ost for Exchange/Microsoft 365. Error 0x8004060c means that file has hit its size limit (50 GB on modern Outlook), so Outlook has nowhere to put new messages and Send/Receive fails. The same error can also appear if the file has become corrupt.
Importantly, deleting emails does not immediately shrink the file. Outlook holds onto that space until you tell it to compact - which is exactly why the error can persist even after you have cleared out old mail. The reliable fix is: clear real space, empty Deleted Items so it actually leaves the mailbox, then run Compact Now to reclaim the space on disk.
Back up first if you can. For a POP account the .pst on your PC may be the only copy of older mail, so it is worth copying it somewhere safe before major cleanup. For Exchange/Microsoft 365 (and most IMAP) accounts the mail lives on the server, so the local .ost is only a cache - it re-downloads from the server and can be safely rebuilt.
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Step by step
How to fix 0x8004060c in classic Outlook
Work through these in order - the first three genuinely free space, and Compact Now is what makes the error clear.
- Empty Deleted Items and Junk. Right-click the Deleted Items folder and choose Empty Folder, then do the same for Junk Email. Until you empty them, those messages still count towards the size.
- Remove the biggest items. Use File > Tools > Mailbox Cleanup > Find items larger than, or sort a folder by Size, to spot large attachments. Delete or save-then-delete the worst offenders - a handful of big attachments often accounts for most of the file.
- Empty Deleted Items again after that clear-out, so the space is genuinely released from the mailbox.
- Compact the data file (the key step). Go to File > Account Settings > Account Settings > Data Files tab. Select your data file, click Settings, then in the Outlook Data File window click Compact Now. This physically shrinks the file to match its real contents. It can take a while on a large file - let it finish.
- If it is a Microsoft 365 / Exchange account, check the mailbox online. The error can reflect the server mailbox being full. Sign in to Outlook on the web and clear space, or check your storage - your provider or we can confirm your quota.
- Still erroring? Repair the file with scanpst. Close Outlook completely. Search for Outlook, right-click it and choose Open file location, then find SCANPST.EXE in the Office folder (typically Program Files > Microsoft Office > root > Office16). Run it, click Browse to select your .pst, then Start. If problems are found, click Repair. It offers to back up the file first - always accept that.
If the file is very large or scanpst reports errors it cannot fix, stop there and let us handle it - a badly bloated or damaged data file is easy to make worse, and we can rebuild it safely without losing mail.
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Frequently asked
What does 'the message store has reached its maximum size' mean?
It means your Outlook data file - the PST or OST that stores your email on the PC - has hit its size limit (50 GB on modern Outlook), so there is no room for new messages and Send/Receive fails. The same error can also appear when that file has become corrupt.
I deleted loads of emails but the error is still there - why?
Deleting mail does not immediately shrink the data file; Outlook keeps the space until you compact it. Empty Deleted Items so the messages truly leave the mailbox, then run File > Account Settings > Data Files > Settings > Compact Now to reclaim the space and clear the error.
Will I lose emails fixing this?
Not if you are careful. Emptying Deleted Items removes only what you have already deleted, and Compact Now just reclaims empty space. For a POP account your PST may be the only copy, so back it up before major cleanup. For Microsoft 365/Exchange the mail is on the server and re-downloads if the OST is rebuilt.
What is scanpst and is it safe to run?
SCANPST.EXE is Microsoft's built-in Inbox Repair Tool for fixing a damaged PST. It is safe and it offers to back up your file before repairing - always accept that backup. Run it with Outlook fully closed. If it reports errors it cannot fix, stop and ask us before going further.
My account is Microsoft 365 - does the same fix apply?
Partly. Compacting the local file still helps, but with 365/Exchange the local OST is only a cache and the error can mean the server mailbox is full. Check your storage in Outlook on the web and clear space there. We support Windows and Android and can check your 365 mailbox with you remotely.
Can 365 Techies fix 0x8004060c for me?
Yes. We connect with your permission using Splashtop SOS - you watch throughout, we phone you first, and access ends the moment your email is flowing again. We will free space, compact and, if needed, safely repair the file. Call 01202 775566.
Mailbox full and no new email?
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