For my group this isn't a want, it's a definite need. My users willTo be clear, Groups.io is sending their own posts back. Whether they can see the returned messages in their email service depends on the service. For Gmail not, usually, but there's a lot of confusion out there about work-arounds to the problem.
I don't know about Wiggio, but the same issue is a perennial topic in Yahoo Groups help lists.
I think for us what would work best is to have it as the ability to setI disagree. The issue email service specific not group specific; so the tools to resolve it belong with the member's profile or subscription not the group settings.
Also, another user in my test group is on gmail and she's getting copiesIt is caused by Gmail, and some other services. But there are various ways to get around it and so some people report that they do get copies back. Much more detail is needed to understand the situation.
Another tester is on AOL and she seems to be getting her messages backShe should look in her spam folder for the occasionally not. AOL and Yahoo Mail are both prone to putting list messages in spam, especially when the From address is your own.