...
Log in to your Confluence instance as an administrator.
Click the admin dropdown and choose Atlassian Marketplace. The 'Find new apps' screen will be displayed.
Use the search function to locate 'E-Mail this Page'. The correct app version will be shown in the search results.
To start the app click on 'Install' and the app starts downloading.
Allowed groups
Select which groups will be allowed to send e-mails. If the setting is not configured, by default all groups will be able to send e-mails.
Allowed domains
Allow only specific domains that the e-mail can be sent to.
Send to groups
Add a extra option to send email to groups.
Configure custom CSS for the e-mails
...