Calendar Meeting issues

Hi Community
Faced with an issue in Calendar. v13.7
Created a calendar meeting to run once , added five employees , only three received the notification via email set to “public”. We checked spam and junk no emails for the other two.
Created a new calendar meeting set it run daily recurring , added three employees. Those three did get the email notification but so did all other users …

Can not see any steps in the docs that i have missed or did incorrectly.

Has anyone faced a similar problem and can shed some light ?

Am i missing something here ?