devise.rb

config/initializers/devise.rb :

config.mailer_sender = "mail-to-send@from.com"
config/environments/production.rb :

config.action_mailer.default_url_options = { :host => 'your.websitedomain.com' }
ActionMailer::Base.smtp_settings = {
  :address        => "smtp.sendgrid.net",
  :port           => "25",
  :authentication => :plain,
  :user_name      => ENV['SENDGRID_USERNAME'],
  :password       => ENV['SENDGRID_PASSWORD'],
  :domain         => ENV['SENDGRID_DOMAIN']
}