That could be good for new feature request to work with the default groups, at least for the administrator, staff, and moderator groups would make sense for this to work.
Wouldn’t make too much sense for TL 0 / Everyone groups to have an e-mail-in address receiver, but there could be some use-cases for that.
At least for this guide would be helpful to mention that currently this is only for created groups, that is not clear from the way this is written:
That is a wiki post but I can’t edit that myself as a new member account here.
Don’t know what kind of budget it would take to sponsor a new feature development for this, seems like may not be that complicated/difficult but also potentially better left as is?