My experience is this:
Find your global npm root folder
npm -g root
Then navigate to the node-red/node_modules
folder below that.
Then
npm uninstall --unsafe-perm node-red-node-email
Restart node-red (you get a warning the module is missing), then install it via the palette manager. Also fully refresh the browser window (shift refresh).
You will find the same issue with the -rbe and the -twitter node.
YMMV