An email address for your whole group.
See: What is group email?
You have complete control over who can send an email to your group. The options are:
To prevent outsiders from spamming the group, we recommend restricting it at least the second option. You have the option of Muzodo forwarding unauthorized emails to a member in the group for moderation. If the email is ok, that group member can resend it.
If you need to allow someone to email the group that is not in the group, you can add them to the white list.