I think this is probably more an outlook bug than a gio bug, but I figured it was still worth bringing up here to see if anyone else has seen this behavior before.
Scenario:   A list member forwarded a g-cal invite to one of our lists. 

Result: 

• In Gio- As expected the message displays as sent from the list member
• In gmail - As expected the message displays as sent from "<list member> via lists.lfnetworking.org to lfn-odl-onap-collab"
• In outlook - unexpectedly the message displays send from "lfn-odl-onap-collab@... on behalf of <original sender>"  rather than on behalf of the list member.

It is worth pointing out that the <original sender> does also happen to be a list member, although the original email that was forwarded to the list was a private email sent outside of any Gio mechanism or control and and had never previously been sent to the list in any form. 
Also worth noting, in this case there isn't a policy/security concern that a private email was forwarded to the list. Not an issue. Don't need any feedback on that aspect of it. ;-)

Thoughts?

--
Kenny Paul, Technical Program Manager for ONAP
The Linux Foundation
Pacific Time Zone