Per TAC SR618314575
As discussed earlier , I had discussions with My development team and here is the response I got from them
This is working as designed – you can include the message count but not the list of unread messages in the body of the email as Unity did – Unity did this because it did not know which message triggered the notification, only that a new message event (or a remaining new message was still pending) was fired so it offered the option to send them all.
Connection’s mail system is more tightly integrated, of course, so the individual message that fired the event is known and can be included in the notification.
There is no documentation that specifically says it doesn’t work like Unity does – the help for SMTP notification notes all the options and does NOT indicate that there is an option to send a list of message headers – hence that’s your documentation proof.