From @abesamma on his other gmail account:
Unfortunately, mailing lists and Discourse can’t handle this. I’d love if this worked, but the email has to come “from” your email address in order to be accepted by Google.
What we’ve done is subscribed a special email address to the group, and so it sends all the emails here where they get posted, trusting the original author info.
This might be something that someone could write a Discourse plugin for. I don’t know if Google Groups has a good API. This would be a pretty big job of both extending the email parsing and ingestion code. So while coding is always possible, let’s call this infeasible.
I think the big question is: how long do the two systems run in parallel?
And, what features or tasks need to be completed before the switch over?
These questions is something that I’d like to see a group form, to work through, and list the steps needed. I can help with this, but we’re going to need some more volunteers.
From Jeremy’s feedback on the call, he didn’t seem to think that importing the Google Group would add value. It still exists and can be searched. So that’s one less “must do” before switching.