The Outlook invitation request mails get deleted from the Inbox of the recipient mail accounts in each of the following scenarios on Outlook.com/ Office 365 Exchange calendar accounts:
1.) when the invite acceptance is done on the web browser after opening the email on outlook.com or owa accounts; or
2.) when the invite acceptance is done on the web browser after opening Outlook calendar on outlook.com or owa; or
3.) when the invite acceptance is done from the Email portion of Outlook desktop client or Outlook mobile app for iOS by clicking accept buttons inside the email body; or
4.) when the invite acceptance is done on the native calendar app of iOS or any other Calendar app like Google Calendar configured as Exchange accounts.
The above auto deletion scenario happens even if the option for "Delete Invitations and Responses that have been updated" has been disabled on the settings of outlook.com on the web under https://outlook.live.com/owa/?path=/options/calendarprocessing.
The situation when auto deletion of email invites does not happen is:
1.) when the invite acceptance is done in a desktop outlook client with the auto deletion option disabled in the desktop outlook client configuration under File> Options> Mail.
2.) when the invite acceptance is done from the "Calendar" portion of Outlook client app for iOS.
This implies that the configuration for disabling auto-delete is not working on outlook.com or owa Exchange servers and is just a cosmetic feature with no consequence.
Kindly advise if it is possible that the option on the web version of Outlook.com or owa for disabling auto deletion actually disables the auto-deletion of mails instead of being just a cosmetic feature with no effect of working, and a similar provision is made in Outlook.com for the Calendar apps like iOS Calendar or Google Calendar to access outlook.com and not delete the event invitation emails upon acceptance.