Top 6 Fixes for Microsoft Outlook Out of Memory or System Resources Error on Windows

Does Microsoft Outlook keep showing the ‘Out of memory or system resources’ error on your Windows 10 or 11 PC? If so, it’s certainly a cause for concern. It can lead to Outlook closing unexpectedly, and disrupt your workflow.

Several factors can influence Microsoft Outlook’s performance on Windows, including the amount of RAM available on your computer, the size of your mailbox, the number of data files, and more. To help out, we have listed all the possible solutions for fixing this Outlook error.

1. Close Background Apps and Programs

A common cause of the Microsoft Outlook out-of-memory issue is running too many apps and programs in the background. To start, you can use the Task Manager on Windows to identify apps and programs using a significant amount of your PC’s memory and close them.

Step 1: Press the Control + Shift + Escape keyboard shortcut to launch the Task Manager. On the Processes tab, click the Memory header to sort apps based on their RAM usage.

Step 2: Select the program you don’t need and click the End task button at the top. Repeat this step to close all the unwanted apps and programs.

This should help free up memory on your PC and prevent Microsoft Outlook from showing errors like ‘Out of memory or system resources’ or ‘System resources are critically low.’

2. Run the Inbox Repair Tool

Damaged or corrupted PST or OST files can also cause Outlook to run out of memory on your Windows computer. Fortunately, Microsoft Outlook includes a tool that automatically repairs your data files. Here’s how to run it.

Step 1: Press the Windows + E keyboard shortcut to open File Explorer and navigate to the following folder.

C:\Program Files\Microsoft Office\root\Office16

Step 2: Double-click the SCANPST.EXE file.

Step 3: Click Start to initiate the scan.

Step 4: Click the Repair button if the tool finds any issues.

3. Remove Unwanted Outlook PST Files

Too many PST files, especially large ones, can affect Outlook’s performance and cause it to display the ‘Out of memory or system resources’ error on Windows. To avoid this, you can consider removing unnecessary PST files using these steps:

Step 1: Press the Windows + R keyboard shortcut to open the Run dialog box. Type control in the text field and press Enter.

Step 2: Change the view type to Large icons and select Mail (Microsoft Outlook).

Step 3: Click the Data Files button.

Step 4: Select the PST file you don’t need and click the Remove option.

4. Reduce Memory Cache Size for Outlook Data Files

If you don’t want to delete any Outlook PST files, you can reduce the memory cache size for those data files to fix the problem. Since this process involves modifying the registry files, you should back up all the registry files or create a restore point before proceeding. That will allow you to restore the registry to its previous state if something goes wrong.

Step 1: Close the Outlook app on your PC.

Step 2: Click the search icon on the taskbar, type in registry editor, and select Run as administrator.

Step 3: Select Yes when the User Account Control (UAC) prompt appears.

Step 4: In the Registry Editor window, paste the following path in the address bar at the top and press Enter.

HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Outlook\PST

Step 5: Right-click on the PST key, go to New, and select DWORD (32-bit) Value. Name it UseLegacyCacheSize.

Step 6: Double-click the UseLegacyCacheSize DWORD and change its value data to 1. Then, click OK.

After completing the above steps, restart your PC and check if the error still occurs.

5. Increase the Size of the Memory Heap

Another thing you can do is increase the size of the memory heap for Microsoft Outlook, which will allow the program to use more memory during runtime. This process also requires you to edit the registry files, so follow the instructions carefully.

Step 1: Press the Windows + R keyboard shortcut to open the Run dialog box. Type regedit in the box and press Enter.

Step 2: Select Yes when the User Account Control (UAC) prompt appears.

Step 3: Paste the following path in the address bar at the top and press Enter:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows Messaging Subsystem

Step 4: Right-click on the Windows Messaging Subsystem key, go to New, and select DWORD (32-bit) Value. Name it SharedMemMaxSize.

Step 5: Double-click the newly created DWORD. Type 300000 in the Value data field and click OK.

Step 6: Right-click on the Windows Messaging Subsystem key, go to New and select Key. Name it Applications.

Step 7: Right-click on the Applications key, go to New and select Key. Name it Outlook.

Step 8: Right-click on the Outlook key, go to New, and select DWORD (32-bit) Value. Name it SharedMemMaxSize.

Step 9: Double-click the SharedMemMaxSize DWORD, type 300000 in the Value data field, and click OK.

Restart your PC after completing the above steps. Following that, Microsoft Outlook should not display the ‘Out of memory or system resources’ error on your Windows 10 or 11 PC.

6. Run the Office Repair Tool

Finally, you can run the Microsoft Office Repair Tool if all else fails. It can help fix performance issues of any Office app, including Outlook.

Step 1: Press the Windows + R keyboard shortcut to open the Run dialog box. Type appwiz.cpl in the box and press Enter.

Step 2: In the Programs and Features window, select the Microsoft Office product on the list and click the Change button at the top.

Step 3: Select the Online Repair option and click Repair.

Make Memory Errors a Thing of the Past

Microsoft Outlook can be a bit of a resource hog at times. However, it can be frustrating if Outlook keeps closing unexpectedly and displays errors such as ‘Out of memory or system resources’ or ‘Outlook has exhausted all shared resources.’ Hopefully, one of the above tips has helped resolve the issue.