You have to set the domain correctly. Currently in the code posted its “mydomain.net”. Change it to gmail.com if you want to sent it via gmail.
config.action_mailer.smtp_settings = {
address: 'smtp.gmail.com',
port: 587,
domain: 'gmail.com',
user_name: '[email protected]',
password: 'yourpassword',
authentication: :plain,
enable_starttls_auto: true
}