How to reproduce: Your server administrator has limited the number of items you can open simultaneously

Question

How to get this error message in Outlook 365?

Your server administrator has limited the number of items you can open simultaneously. Try closing messages you have opened or removing attachments and images from unsent messages you are composing.

I've created an Outlook plugin and it work just fine on my PC/Exchange account, but on my customer PC it crash with this error.

I'm using some LINQ queries and according to this post I shouldn't. Now I would like to test the fix on my PC before going to my customer, but I cannot find out how to generate this error...

Answer 1

Turn cached mode off in your Exchange account settings and make sure you are working against a folder with a larger number of messages (> 250, or even thousands).

And yes, do not use LINQ or plain loops against the Items collection - use Items.Find/FindNext or Items.Restrict .