How to email all user group members.
Need to email your group members?
When setting up an event registration, your group members will not automatically receive an email invitation. In order to invite members to your meeting, you can use the "Email Group Members" capability in the "Settings" area of the user group homepage.
From there you can select "All Group Members" and type your message. The "Subject" will be automatically populated to say "Message From" but you can treat this field like a subject line.