Additional sender list
Here's a more granular way to select who can send to your group. You can allow specific non-group members to send messages. They won't receive group messages, but they will receive replies to their messages as threaded conversations.
Login, click to select the group where you want to make changes, click Settings:
Scroll down to Message Flow and click Manage additional senders:
Click Add to either add individual email addresses (1), or allow anyone from a specific domain (2) by adding *@domain (as a wildcard email address):
Click Add additional senders and Gaggle Mail shows you the added email addresses/wildcards:
