Easily remedied:
Can someone apply this?
[safe4all-staging@safe4all www]$ tla file-diff message-email.tcl
--- orig/packages/forums/www/message-email.tcl
+++ mod/packages/forums/www/message-email.tcl
@@ -12,6 +12,9 @@
forum::security::require_read_message -message_id $message_id
+# Require a login. Otherwise, people can use this for spamming
+auth::require_login
+
# Get the message information
forum::message::get -message_id $message_id -array message
set message(tree_level) 0