Make sure you have Google 2-Step Verification turned on: https://www.google.com/landing/2step/

As explained in this article: https://support.google.com/accounts/answer/185833?hl=en, create an application specific password, "App Password", 'my-app-password' below, for your SMTP connection: https://security.google.com/settings/security/apppasswords

Now you can use the following mail settings:

Mailer SMTP
SMTP Host smtp.gmail.com
SMTP Port 587
SMTP Security STARTTLS
SMTP Authentication Yes
SMTP Username This email address is being protected from spambots. You need JavaScript enabled to view it.
SMTP Password my-app-password