I'm not fully convinced with deleting the module folder part. This is what I did:
sudo npm uninstall -g node-red-node-email
and it outputs:
up to date in 0.038s
which means uninstall did nothing.
later I called:
sudo npm ls -g node-red-node-email
and it outputs:
/usr/lib └─┬ node-red@0.19.2 └── node-red-node-email@0.1.29
then I removed the module folder as you suggested:
sudo rm -r /usr/lib/node_modules/node-red/node_modules/node-red-node-email
and re-printed the module status, and this time I get the following:

As I pointed earlier, node-red keeps track of installed modules and deleting the module-folder just like that doesn't seem the right way.