If you want to use Gmail SMTP from QlikView NPrinting you will need to set Allow less secure apps to ON.
This is how I managed to get it working. If you choose to do the same you do so at your own risk.
1. Log into the Google account that you are using to send e-mails from NPrinting https://myaccount.google.com/intro
2. Click on Connected apps & sites
3. Switch Allow less secure apps to ON
HTH - Daniel.