Action "Send email" fails to redirect to mail contact form

When using action "Send email" in a public viewable profile,
the user gets an
"Error:
Page access denied! Please login or register"

Goal: Unregistered users should be able to send a mail using the mail form to the choosen CB community user, as long as this CB user has published its mail address.

(Original message in German:
Fehler
Kein Zugriff auf diese Seite! Bitte voher anmelden oder registrieren.
)

You need to enable public access to the email form within CB > Configuration > General if you want unregistered users to be able to send emails.