Out of memory when opening a pst-file

I’ve got a fair amount of Personal Folder (pst-files) connected in Outlook and I wanted to add another one. When I tried, I got the following error;

“Out of memory or system resources. Close some windows or programs and try again.”

My system has lots of memory (4GB) and still plenty of memory free but even after closing all other applications and restarting my computer, I still get the same error.

How can I open more pst-files?

PST buttonWhen Outlook connects to a pst-file, it stores and reserves as certain portion of memory as a cache to increase performance. For this, Outlook only has a certain amount of address space available and it is this “memory or system resource” that Outlook has run out on.

To solve this issues there are 2 main solutions;

  • Decrease the amount of pst-files that you have open in Outlook
  • Decrease the memory cache-size per pst-file via the Registry

Out of memory or system resources. Close some windows or programs and try again.
After opening 93 pst-files in Outlook, I was able to reproduce this error…

Outlook has exhausted all shared resources, please close all messaging applications and restart Outlook (example: Skype for Business).
Outlook 2016, Outlook 2019 and Office 365 show a bit more accurate and helpful error.

Solution 1: Decrease the amount of pst-files that you have open in Outlook

Close PST-File buttonAs you will only run into this problem when you have more than 15 pst-files of a considerable size (1GB or more) connected in Outlook or over 50 medium/smaller sized ones (around 300MB), the practical solution would be to decrease the amount of pst-files that you have open in Outlook.

For instance; Disconnect the pst-files that you are not actively using and consider only to archive to a separate pst-file when the work on that specific project or assignment has been completed (which is often a common reason to use separate pst-files).

Note:
If you’ve got less than 15 pst-files connected in Outlook, then the solutions in this article will not solve your issue. In that case, it is much more likely that you’ll fix your issue by running scanpst.exe against all your pst-files, troubleshooting your add-ins or recreating your mail profile. For additional solutions also see; Outlook doesn’t start.

Solution 2: Decrease the memory cache-size per pst-file via the Registry

Regedit buttonIf there is no way to reduce the amount of pst-file that you need to have connected to Outlook and you are running into this error, then you can reduce the amount of memory cache that Outlook allocates to each connected pst-file via a Registry change;

Key: HKEY_CURRENT_USER\Software\Microsoft\Office\<version>\Outlook\PST
Value name: UseLegacyCacheSize
Value type: REG_DWORD
Value: 1

Note: After applying this Registry change, Outlook’s performance will decrease as fewer read/write operations will now be cached.

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