I have posted this in the MS support forum but there has been no response so I thought I'd try here in the hope of getting some ideas.

Further to the description, below, Outlook only runs out of resources when there's also a fairly large Excel workbook open (any one of several , it isn't specific to a particular Excel workbook). Excel itself never reports a lack of resources, but closing the Excel workbook makes Outlook happy again !

Problem description



I have a straightforward installation of Office 365 on Windows 11. Usually there's not much else running except Google Chrome and sometimes a large Excel workbook or small-ish Word documents or a photo editor.

6 months ago I started getting messages that Outlook had run out of shared resources and that I should close any messaging applications.

I wan't able to fix it that and had to restart Windows to get Outlook going again.

Then the problem went away - I am not aware of any system or application changes around that time.

A week ago it came back again and now it forces me to do a restart every few hours, sometimes more often, which is a real pain.

How can I set about diagnosing the cause ?

The only relevant thing I have thought of is to check RAM usage but I always seem to have at least 7GB free out of 16GB in total.

When there isn't the resource problem, Outlook is behaving just fine.

Solved
The issue was the CompanionLink software whose synch was set to "daily". his was keeping the Outlook process running even when Outollk was apparently closed.
I have set the synch to "manual" (not a big deal for me) and have had no further issues.