Prevent Microsoft 365 meeting invites from automatically appearing in users’ calendars

That option "automatically process meeting requests..." as far as I know is unchecked by default and also does not work to counter meeting request spam. The meeting will still be added to your calendar as "tenative" and this is "by design" from MS. User posted his settings, showing that setting as unchecked and still gets meeting/calendar spam, also as soon as you select the message or view it in the reading pane it will be added to yoru calendar as tenative despite that setting. An Exchange Transport rule might be your only option.

Reference:

https://learn.microsoft.com/en-us/answers/questions/4729168/outlook-automatically-accepting-scam-meeting-invit

https://kb.uwm.edu/uwmhd/45596

https://learn.microsoft.com/en-us/answers/questions/5558001/how-to-prevent-calendar-invites-from-external-sour