How to Fix Microsoft Outlook “Out of Memory or System Resources” Errors on Windows

The Microsoft Outlook “Out of Memory or System Resources” error usually appears when Outlook cannot allocate enough memory or Windows resources to complete an action. It can happen when opening large emails, switching folders, starting Outlook, or working with a damaged mailbox or add-in.

In many cases, the problem is not a true lack of RAM. It is often caused by a corrupted Outlook profile, a problematic add-in, oversized data files, or a 32-bit Outlook installation that is running into limits.

1. Start Outlook in Safe Mode and Disable Problematic Add-ins

A faulty add-in is one of the most common causes of Outlook resource errors. Safe Mode loads Outlook without add-ins, which makes it easier to confirm whether one of them is causing the issue.

1. Press Windows + R.
2. Type outlook /safe and press Enter.
3. If Outlook opens normally in Safe Mode, go to File > Options > Add-ins.
4. At the bottom of the window, choose COM Add-ins and click Go.
5. Clear the checkboxes for add-ins you do not need, then restart Outlook normally.
6. Re-enable add-ins one at a time until the error returns, which helps identify the cause.

2. Reduce the Size of Your Mailbox and Outlook Data File

Large mailboxes and oversized PST or OST files can make Outlook slower and more likely to hit resource limits, especially when opening folders with thousands of items or handling very large attachments.

1. Empty Deleted Items and Junk Email folders.
2. Delete or archive old messages that you no longer need.
3. Save large attachments to disk instead of keeping them in email.
4. Use Search Folders or archive folders to keep active mailboxes smaller.
5. If you use a PST file, compact it through Account Settings > Data Files > Settings > Compact Now, if that option is available.

3. Repair Your Outlook Profile or Create a New One

A damaged Outlook profile can cause resource-related errors even when the rest of Windows is working properly. Creating a new profile is often one of the most effective fixes because it gives Outlook fresh account settings and configuration files.

1. Close Outlook.
2. Open Control Panel and search for Mail.
3. Select Mail (Microsoft Outlook) to open Mail Setup.
4. Click Show Profiles.
5. Choose Add to create a new profile and set up your email account again.
6. Set the new profile as the default profile, then start Outlook and test it.

4. Repair Office or Update Outlook

If Outlook program files are damaged or outdated, resource errors can show up during normal use. Repairing Office can replace broken files, while updates may fix known bugs that affect memory usage or compatibility.

1. Open Settings > Apps > Installed apps.
2. Find Microsoft 365 or Office and select Modify or Change.
3. Run the Quick Repair first.
4. If the issue continues, run Online Repair for a deeper fix.
5. After that, open Outlook and check for updates through File > Office Account > Update Options.

5. Use 64-bit Office if You Work with Large Mailboxes or Files

If you are using 32-bit Outlook on 64-bit Windows, Outlook may run into memory limits sooner than the 64-bit version. This is especially noticeable with large mailboxes, many calendar items, or heavy use of add-ins.

1. Open Outlook and go to File > Office Account > About Outlook to check whether it is 32-bit or 64-bit.
2. If you are on 32-bit and regularly see this error, consider uninstalling and reinstalling the 64-bit version of Office.
3. Back up important Outlook data before reinstalling, especially if you use local PST files.
4. After switching versions, reinstall any required add-ins and confirm that your accounts sync correctly.

How to Narrow Down the Cause

If none of the fixes above solves the problem completely, the error may be tied to a specific folder, message, or account rather than Outlook as a whole. Try opening Outlook with a different mailbox, temporarily removing shared mailboxes, or testing whether the error appears only when you open a particular folder or email.

• If the error happens only with one folder, the folder may be damaged or overloaded with items.
• If it happens only with one message, the email may contain a large attachment or malformed content.
• If it happens only after Outlook has been open for a long time, an add-in or memory-heavy workflow is more likely.
• If it happens during startup, profile corruption or a bad add-in is usually a stronger suspect.

When Outlook Still Will Not Open Properly

If Outlook is completely unusable after the basic fixes, the next best step is usually to create a new profile, repair Office, and make sure Windows and Office are fully updated. If your data is stored in PST files, back them up before trying more aggressive cleanup steps.