gmail_sender.rb

require 'pony'

=begin
    Use gmail's smtp server to send email:
    1. Turn on 2-Step Verification (see https://myaccount.google.com/security)
    2. Sign in using App Passwords (see https://support.google.com/accounts/answer/185833?hl=en)
    
    or alternative method:
    1. Turn off 2-Step Verification (see https://myaccount.google.com/security)
    2. Allow less secure apps: https://myaccount.google.com/u/0/lesssecureapps?pli=1

    here we use the alternative method(Allow less secure apps, use the same login password)
=end

Pony.mail({
  :to => 'foo@bar.com',
  :subject => 'test subject',
  :html_body => 'Allow less secure apps <div style="color:red;">hello I am sent via gmail smtp server</div>',
  :via => :smtp,
  :via_options => {
    :address              => 'smtp.gmail.com',
    :port                 => 587,
    :enable_starttls_auto => true,
    :user_name            => 'the-account-name@gmail.com',
    :password             => 'the-password',
    :authentication       => :plain 
  }
})

see https://support.google.com/accounts/answer/6010255?hl=en