By default, Google Groups are closed and require membership to email the group. There are cases where this isn’t ideal, such as:
- using the email for social media accounts
- creating a department email that people from other organizations can email
If you are using the group to receive public emails these settings.
Permissions > Basic permissions
- Post: Public
Settings > Moderation
- Spam messages: Skip the moderation queue and post to the group
The first setting is required and the second optional, but random legitimate messages tend to get caught in the Spam filters.