Group email address: Overview
What is the group email address?
The email address people used to send messages to a group.
You can view this when opening Home:

Can I change the group email address?
Yes, you can create a custom domain. This can be the public email address that members use.
Every group also has an email address ending in @gaggle.email, which is automatically created when you create the group.
Can I change the group name?
Yes, at any time. Login and select the group to change.
Click Design in the sidebar and then click Edit next to Group name:

How do I change the subject prefix?
The subject prefix is always the group name. For example, messages to a group called Book Club arrive with subjects like [Book Club] Meeting on Friday.
There's no separate subject prefix setting. To change the prefix, change the group name on the group's Design page, as shown above.