development.rb

# config/environments/development
# ActionMailer Config
  config.action_mailer.default_url_options = { :host => 'localhost:3000' }
  config.action_mailer.delivery_method = :smtp
  # change to true to allow email to be sent during development
  config.action_mailer.perform_deliveries = false
  config.action_mailer.raise_delivery_errors = true
  config.action_mailer.default :charset => "utf-8"
  #config.action_mailer.default_url_options = { :host => 'your.websitedomain.com' }
  config.action_mailer.smtp_settings = {
    address: "smtp.sendgrid.net",
    port: 25,
    domain: "heroku",
    authentication: "plain",
    user_name: ENV["SENDGRID_USERNAME"],
    password: ENV["SENDGRID_PASSWORD"]
  }

devise.rb

#config/initializers/devise.rb
config.mailer_sender = "ENV['SENDGRID_USERNAME']"

mail.rb

#config/initializers/mail.rb
ActionMailer::Base.smtp_settings = {
  :address        => 'smtp.sendgrid.net',
  :port           => '587',
  :authentication => :plain,
  :user_name      => ENV['SENDGRID_USERNAME'],
  :password       => ENV['SENDGRID_PASSWORD'],
  :domain         => 'heroku.com'
}
ActionMailer::Base.delivery_method = :smtp