"Send Cancellation" triggers OnAppointmentSend launch event in Classic Outlook and not on New or Web Outlooks

[pepso]

Your Environment

• Platform: Desktop
• Host: Outlook
• Office version number: Classic Outlook / Version 2408 Build 16.0.17928.20114 64-bit
• Operating System: Win 11

Expected behavior

When cancelling an appointment on Classic Outlook, it is expected OnAppointmentSend LaunchEvent add-in behaves the same as New Outlook + Web Outlook. OnAppointmentSend is not triggered for New/Web Outlook.

Current behavior

When choosing to cancel an appointment and clicking "Send Cancellation" the OnAppointmentSend launch event is triggered.

This is not the case for New or Web Outlooks.

Steps to reproduce

Classic Outlook:

1. Create an appointment with a distribution list and send it to participants.
2. Open the appointment and choose "Cancel Meeting" from the ribbon
3. Click "Send Cancellation" and observe the add-in WILL get triggered

New / Web Outlook:

1. Create an appointment with distribution list and send it to participants.
2. Open the appointment and choose "Cancel" from the ribbon
3. Click "Send" and observe the add-in IS NOT being triggered

Provide additional details

This is problematic because we are not aware of any field/indicator of the appointment object which would tell us the appointment is "cancel" type so we can work around the problem.

We have observed { launchEventType: 6, type: 'Unknown' } being triggered as part of our tests and we are wondering if this has something to do with event cancellation?

Context

Our Add-in is used to help appointment organizers to validate their meeting details during the drafting / sending time and we provide Smart Alert guidance to user about their appointment. This is obviously not desired guidance when people on the Classic Outlook cancel their meetings from the calendar. Because we don't have a way to check if this is event cancellation we don't know when to respond allowEvent:true and when to prompt user and actually apply our appointment logic.

We would love to have all Outlook versions to behave the same, but we are happy to rely on some field / launch event's event object parameter / item's data field indicating us this is a cancellation appointment on Classic Outlook.

We found a historical comment there is no launch events for cancelling so we are wondering if some regression have taken place #3588 (comment)