I think
@AndreasPo_3CX has provided a very rational solution. Surely, you do not have many outside parties that need to receive notifications? Creating a single dummy extension that you hide from the rest of the PBX seem like a reasonable approach.
As a programmer myself, I recognize the value in having one place to maintain email addresses, and have that address applied throughout the system (user's extension). The more "features" you add to software, the more opportunities for bugs, and the more things the QA team has to test. 3CX is designed with a focus on simplicity and ease of use. The alternative is to work with a phone system like LG Ericsson that has so many "features" that they gave up trying to provide a workable UI and you access "features" by entering a feature code in a search field. Can you imagine?
I understand that this suggestion seems like a small thing, but you must recognize that 3CX gets lots of "little" suggestions every day, and if they did them all, we would end up with an LG Ericsson, and we don't want that.
But when you get into a situation where you simply cannot live without a feature, 3CX provides a wealth of tools for building custom solutions (3CX Call Flow Designer, XAPI, and Call Control API). It is, in fact, that broad support for customization that brought us to the 3CX ecosystem. For example, if you need external notifications for missed or abandoned calls, or when callers waiting in the queue exceed thresholds, or simply that another person has joined the queue, our
3CX Queue Notifier can notify you by paging, email, SMS text, and desktop popup. That's the kind of customization you can create with 3CX.