app.rb

post '/contact' do
 configure_options
 Pony.mail(
    :from => [params[:name], "<", params[:email], ">"].join,
    :to => 'hi@mydomain.com',
    :subject =>  ["Opt-in via /contact: ", params[:name]].join,
    :body => [params[:name], params[:email]].join(": ")
  )
  redirect '/'
end

def configure_options
  Pony.options = {
    :via => :smtp,
    :via_options => {
      :address              => 'smtp.sendgrid.net',
      :port                 => '587',
      :domain               => 'heroku.com',
      :user_name            => ENV.fetch('SENDGRID_USERNAME'),
      :password             => ENV.fetch('SENDGRID_USERNAME'),      
      :authentication       => :plain,
      :enable_starttls_auto => true
    }
  }
end