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