Troubleshooting “Folder size limit exceeded”

When organizing emails or running mail migrations, you may see an error like “Folder size limit exceeded,” “Mailbox size limit exceeded,” or “Maximum folder size reached.” This happens when an email directory passes the maximum storage or message-count threshold allowed by your local client or your email provider.

Quick Answer

The “Folder size limit exceeded” error occurs when a single local folder hits its file-system size boundary (such as Outlook’s 50 GB PST/OST file limit) or when an IMAP folder exceeds Google’s message limits during synchronization. To fix it, split messages into sub-folders, compact local data files, or raise file-size limits in the Windows Registry.

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Why Folder Size Limits Are Triggered

"Folder Size Limit Exceeded"
│
├── Is the error coming from Microsoft Outlook desktop?
│   ├── YES ──► Local .PST/.OST data file reached its 50 GB threshold.
│   └── NO  ──► Server-side or migration tool threshold.
│
├── Is the error occurring during a cloud migration (e.g., GWMMO/GWMME)?
│   ├── YES ──► Google Workspace folder limit (max items per label hit).
│   └── NO  ──► Webmail quota reached (account out of storage).

1. Outlook 50 GB Local File Limit

By default, modern versions of Microsoft Outlook (2016, 2019, 2021, and Microsoft 365) cap individual offline storage files (.ost and .pst) at 50 GB. Once a folder’s local database reaches this ceiling, Outlook blocks incoming mail, stops syncing, and generates folder-limit errors.

2. Google Workspace Item and Label Thresholds

While Gmail allows mailboxes to scale with your paid storage tier, its indexing engine struggles when too many messages share a single label:

• Single folders containing more than 100,000 messages can cause API timeouts and migration failures.
• Migration utilities like GWMME (Google Workspace Migration for Microsoft Exchange) or GWMMO will stop importing and report folder limit warnings when a single directory exceeds allowed thresholds.

3. Account Storage Quota Exhaustion

If your total Google account storage (combining Gmail, Google Drive, and Google Photos) runs out of space, incoming IMAP synchronization will fail, and some clients report this as a folder-level size error.

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Step-by-Step Diagnostic and Resolution Procedure

Step 1: Determine Whether the Limit is Local or Cloud-Based

1. Log into your mail account using your web browser.
2. Check your total mailbox usage at the bottom of the page (e.g., 12.4 GB of 30 GB used).
3. If webmail shows ample storage space remaining, the error is local to your desktop email client. Proceed to Step 2.
4. If webmail displays a red bar or reports Storage Full, purchase additional storage or delete unneeded files. For deep diagnostics on storage usage, see “You have run out of storage” in Gmail but Drive empty.

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Step 2: Increase the Outlook Data File Cap via Windows Registry (Local Outlook Fix)

If you use Microsoft Outlook on Windows and your local data file has reached 50 GB, you can expand the allowable file size to 100 GB using the Windows Registry.

Caution: Back up your registry before making changes. Setting data files above 100 GB can cause performance lag.

1. Close Outlook completely.
2. Press Windows Key + R, type regedit, and press Enter.
3. Navigate to the key corresponding to your Outlook version:
   • Outlook 365 / 2019 / 2016:HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Outlook\PST(Note: If the PST sub-key does not exist under Outlook, right-click Outlook, select New > Key, and name it PST).
4. In the right pane, check for these two DWORD values. If they do not exist, right-click an empty area, select New > DWORD (32-bit) Value, and create them:
   • MaxLargeFileSize
   • WarnLargeFileSize
5. Double-click MaxLargeFileSize:
   • Set the Base to Decimal.
   • Set the Value data to 102400 (this equals 100 GB in megabytes).
   • Click OK.
6. Double-click WarnLargeFileSize:
   • Set the Base to Decimal.
   • Set the Value data to 97280 (this equals 95 GB, giving you a 5 GB warning buffer).
   • Click OK.
7. Close the Registry Editor, restart your PC, and open Outlook.

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Step 3: Compact Outlook Data Files to Reclaim Free Space

Deleting messages from large folders does not immediately shrink the local .ost or .pst file on your disk. You must compact the file to reclaim the unused space:

1. In Outlook, click File > Account Settings > Account Settings.
2. Click the Data Files tab.
3. Select your data file and click Settings.
4. In the dialog that opens, click Compact Now.
5. Wait for the operation to complete (this may take 15–45 minutes for files near 50 GB), then click OK.

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Step 4: Resolve Folder Limits During Data Migrations

If you are migrating legacy mailboxes into Google Workspace and hitting single-folder caps:

1. Divide large source folders into sub-folders grouped by year (e.g., Archive_2022, Archive_2023).
2. Run migration utilities using folder exclusion filters to process smaller batches.

For detailed migration troubleshooting, consult Resolve “Too many items in a single folder” Limits.