How to Fix ‘Outlook Out of Memory or System Resources’ Error in Outlook 2021/2019/2016/365?

The “Out of Memory or System Resources” error when your Outlook does not have enough system memory. This can prevent your email client to perform tasks such as opening a mail folder, loading emails, or syncing mailbox data. If this error appears in Windows Outlook, it can freeze up, crash, slow down or not open folders and emails. This post elucidates the cause of this error and a step-wise procedure to correct the error.

What does the ‘Out of Memory or System Resources’ Error Mean?

This error indicates that your email client is unable to access enough RAM or system resources to complete a task. It commonly occurs Outlook reaches its memory limit, the OST file becomes too large, or add-ins consume excessive memory, then you may encounter this error.

Below are some variations of the error:

Common Causes of “Outlook Out of Memory or System Resources” Error

The table below mentioned the most probable reasons behind the error.

Why 32-bit Outlook Causes Memory Errors?

The Outlook 32-bit edition has a 2 GB memory ceiling. When add-ins, large mailboxes, and multiple open folders together cross this limit, the “Out of Memory or System Resources” error appears. You many need to switch to 64-bit, if you are handling large mailboxes or several add-ins.

Solutions to Fix ‘Out of Memory or System Resources’ Error in Outlook

Follow the below solutions to fix this error in Microsoft Outlook, running on a Windows system. 

Solution 1 — Check if You Are Running 32-bit Outlook

The 32-bit version of Outlook can only use up to 2 GB of memory. If you are managing large mailbox or several add-ins, then your email client may run out of memory. In such a situation, you can switch to 64-bit Outlook to fix this issue. Here’s how:

1. Open Outlook.
2. Click File > Office Account.
3. Click About Outlook.

• Check the application version.

• If it is 32-bit, upgrade to 64-bit version. Here’s how
• Open Control Panel.
• Choose Programs and Features option.

• Then, uninstall Microsoft Office or Microsoft 365.
• Reinstall Office.
• Select the 64-bit version during installation.
• Start your PC again.
• Launch Outlook and check if the problem is solved.

Note: Microsoft 365 and Office 2019 install the 64-bit version by default in most systems.

Solution 2 – Check and Free System Resources using Task Manager

If your Outlook is showing memory-related errors, high RAM usage on your system could be one of the reasons.  You can use Task Manager to check how much memory Outlook and other applications are using your system. Here’s how: 

• Press Ctrl + Shift + Esc.
• If Task Manager opens in the simplified view
• Click More Details.
• Select the Performance tab

• Check the current Memory (RAM) usage.
• If RAM usage is above 85%, switch to the Processes tab.
• Review the list of running processes.

• Identify applications consuming a large amount of memory.
• Right-click any non-essential process
• Select End Task to free up system resources.
• Close Task Manager
• Restart Outlook.

Check whether the error has been resolved.

Note: If your system’s RAM usage consistently remains above 85% even when Outlook is closed, consider upgrading your system memory. Microsoft 365 users with large Outlook mailboxes, 8 GB RAM is the minimum recommended configuration, though 16 GB generally recommended for better performance.

Solution 3 — Restart and Update Outlook

Outdated Outlook version sometimes contains memory leak bugs that trigger memory errors. Restarting and updating Outlook can resolve these issues. Here’s how:

1. Close Outlook completely.
2. Open Task Manager and end all Outlook-related processes.
3. Wait for 2 minutes.
4. Reopen Outlook.
5. Go to File > Office Account.
6. Click Update Options.
7. Select Update Now.
8. Install all available updates.
9. Restart the computer.
10. Open Outlook again.

Updating Outlook fixes several known OST memory allocation issues.

Solution 4 — Increase Virtual Memory

Virtual memory supplement disk space to support physical RAM. Increasing the page file size gives Outlook additional addressable memory. To resolve the “Out of Memory or System Resources” error, you can adjust Virtual Memory in windows. Here’s how:

1. Press Windows + R.
2. Type sysdm.cpl and press Enter.
3. Click the Advanced tab.
4. Under Performance, click Settings.
5. Click the Advanced tab again.
6. Under Virtual Memory, click Change.
7. Uncheck Automatically manage paging file size for all drives.
8. Select the C: drive.
9. Choose Custom size.
10. Set Initial Size to 1.5x total RAM.
11. Set Maximum Size to 3x total RAM.
12. Click Set.
13. Click OK.
14. Restart the computer.

Virtual Memory Values

Note: These values are in MB. 1 GB = 1,024 MB. Do not set Maximum Size above 3x your physical RAM as this can degrade overall system performance.

Solution 5 — Find and Disable Faulty Add-ins

Outlook memory errors may occurs due to problematic add-ins. You can identify and manage these add-ins by running Outlook in safe mode and turning off all add-ins. Once you’ve done that, restart Outlook normally. Then, activate each add-in one by one and observe Outlook for error. If the error appears activating an add-in, deactivate and remove that particular one. Here’s how: Press Windows +R.

• Type Outlook.exe /safe. 
• Click OK or press the Enter key.
• This starts Outlook in safe mode.
• Now, go to File > Options > Add-Ins.
• Click Go.

• Uncheck all add-ins and click OK.
• Close Outlook and start it normally.
• Go to File > Options > Add-Ins. 
• Click Go.

• Check one add-in and click OK to activate it.
• Observe Outlook for the error. If the error does not appear, activate another add-in.
• Repeat the last two steps until you find the faulty add-in and then uninstall it from Outlook.

Common Memory-Intensive Add-ins to Check First

Below are some Memory-Intensive Add-ins to check first:

• Antivirus Outlook plugins: Norton 360, McAfee, Windows Defender Email Scanning
• CRM integrations: Salesforce for Outlook, HubSpot Sales
• PDF tools: Adobe Acrobat PDFMaker
• Collaboration add-ins: Zoom, Teams Meeting

Start by disabling antivirus add-ins first — these are responsible for a large proportion of Outlook memory issues.

Solution 6 — Increase Outlook Memory Heap (Registry Fix)

The SharedMemMaxSize registry value manages the shared memory required for rendering mailbox items such as emails and folders. When this limit is reached due to heavy mailbox environment, Outlook displays “Out of Memory or System Resources” error. You can increase OST size of the memory heap to 300000 in Hexadecimal to fix this problem. Here’s how you can do this:

problem. Here’s how you can do this:

• Close Outlook.
• Press Windows + R.
• Type regedit.
• Then, select OK or hit Enter.
  • Now, go to the following registry key:
  • HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows Messaging Subsystem.
• Click Edit > New. 
• Choose DWORD Value.
• Type SharedMemMaxSize
• Press Enter.
• Then, right-click on SharedMemMaxSize and choose Modify.
• Type 300000 in the value data box. Always use the default Base of Hexadecimal.
• Click OK. 
• Navigate to the following registry subkey:
  • HKEY_LOCAL_MACHINE/SOFTWARE/Microsoft/Windows Messaging Subsystem/Applications/Outlook
•  Again click Edit > New. 
• Choose DWORD Value.
• Type SharedMemMaxSize. 
• Then click Enter.
• Type 300000 value.
• Click OK.

If the issue persists, restart Windows and then launch Outlook again.

Tip: ‘The SharedMemMaxSize registry value is often the last resort fix — it is only needed when a large mailbox, multiple add-ins, and 32-bit Outlook combine to exceed the shared memory pool ceiling.’

Solution 7 — Run Windows Memory Diagnostic Tool

Windows provides a built-in diagnostic tool. This tool checks your computer’s RAM for issues. If the RAM contains faulty sectors, Outlook may continue showing “Out of Memory or System Resources” error even after applying software-level fixes. You can solve this problem by recreating the OST file. This is how it’s done:

1. Press Windows + R.
2. Type mdsched.exe.

• Click OK.
• Select Restart now in the Windows Memory Diagnostic window
• Check for problems.

• Your system will restart automatically and begin the memory test.
• The scan usually takes around 10–15 minutes to complete.
• When the Outlook is restarted, open Event Viewer and navigate to:
  • Windows Logs > System.

• Look for entries named MemoryDiagnostics – Results to view the test results.
• If the tool reports memory errors, the RAM module may need to be replaced.

If no issues are found, proceed to the next solution.

Solution 8 — Rebuild the OST File

If your OST file reaches its maximum size or corrupts, Outlook can use more system memory during folder access and mailbox syncing. This can cause errors like “Out of Memory or System Resources”. This can be resolved by recreating the OST file. Here’s how to:

• Close Outlook.
• Press Windows + R.
• Type %LOCALAPPDATA%\Microsoft\Outlook\ and press Enter.
• Move the .ost file to a different location (for backup).
• Relaunch Outlook — it recreates the OST file automatically from the server. 

Quick Fix Guide — Which Solution to Try First?

The table mentioned below provides a quick overview of each solution. You can use this table to choose the most effective solution according to the situation.

Conclusion

The error “Outlook Out of Memory or System Resources” can slow down the application performance. Due to this, you may not be able to perform certain operations, as the email client stalls or crashes. You can fix such performance issues by following the troubleshooting methods outlined in this post. But if your OST file becomes inaccessible or orphaned, you need to convert it to PST using Stellar Converter for OST – an advanced desktop application. It lets you extract mail items from inaccessible or orphaned and save them as a PST file. You can then import this new PST into your Outlook using the Import/Export Wizard.

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