Hi xMarcus,
Based on your description, I’ve done tests in multiple computers and different account. The registry key won’t take effect on the searching limit. And the search results limited at 1025 after I clear the Improve search speed by limiting the number of results shown (File > Option > Search)checkbox.
And there is no option can remove the search limit in Outlook, the current workaround is switch the search scope to “All Outlook Items” or “All mailboxes”. While I totally understand your inconvenience, I suggest you submit your feedback via the following link:
https://outlook.uservoice.com/forums/322590-outlook-2016-for-windows
Many features of current programs have been designed and upgraded based on customers’ feedback.
Regards,
Huni