Missing host to link to! Please provide :host parameter or set default_url_options[:host]

config.action_mailer.default_url_options = { :host => 'localhost:3000' }

config.action_mailer.default_url_options = { :host => 'mywebsitename.com' }
config.action_mailer.default_url_options = { :host => 'heroku.mywebsitename.com' }

config.action_mailer.default_url_options = { :host => 'yourapp.heroku.com' }

User.create(:username => "test", :email => "test@test.com", :password => "test1234", :password_confirmation => "test1234", :confirmed_at => "2010-11-03 14:11:15.520128")

ActionView::Template::Error: Missing host to link to! Please provide :host parameter or set default_url_options[:host]
/home/slugs/.../mnt/.bundle/gems/ruby/1.8/gems/actionpack-3.0.0/lib/action_dispatch/routing/route_set.rb:473:in `url_for'
/home/slugs/.../mnt/.bundle/gems/ruby/1.8/gems/actionpack-3.0.0/lib/action_dispatch/routing/url_for.rb:132:in `url_for'
/home/slugs/.../mnt/.bundle/gems/ruby/1.8/gems/actionpack-3.0.0/lib/action_view/helpers/url_helper.rb:99:in `url_for'
/home/slugs/.../mnt/.bundle/gems/ruby/1.8/gems/actionpack-3.0.0/lib/action_dispatch/routing/route_set.rb:195:in `user_confirmation_url'

config.action_mailer.default_url_options = { :host => 'yourapp.heroku.com' }

Errno::EAFNOSUPPORT: Address family not supported by protocol - socket(2)
/usr/ruby1.8.7/lib/ruby/1.8/net/smtp.rb:551:in `initialize'
/usr/ruby1.8.7/lib/ruby/1.8/net/smtp.rb:551:in `open'
/usr/ruby1.8.7/lib/ruby/1.8/net/smtp.rb:551:in `do_start'
/usr/ruby1.8.7/lib/ruby/1.8/timeout.rb:62:in `timeout'

config.action_mailer.default_url_options = { :host => 'localhost' }

config.action_mailer.default_url_options = { :host => 'yourapp.heroku.com' }

heroku addons:add sendgrid:free

config.action_mailer.default_url_options = { :host => 'localhost:3000' }

config.action_mailer.default_url_options = { :host => 'yourapp.heroku.com' }

config.action_mailer.default_url_options = { :host => ENV['MAILER_URL'] }

heroku config:set MAILER_URL=my-awesome-app.herokuapp.com --app my-awesome-app

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

  config.action_mailer.default_url_options = { :host => 'YOUR-DOMAIN-HERE.COM' }

Rails.application.routes.default_url_options[:host] = 'myappsname.herokuapp.com'
config.action_mailer.delivery_method = :smtp
config.action_mailer.perform_deliveries = true
config.action_mailer.raise_delivery_errors = false
config.action_mailer.default :charset => "utf-8"

class MyMailController < ApplicationController
  before_filter :set_host_from_request, only: [:create]

  ....

  private
  def set_host_from_request
    ActionMailer::Base.default_url_options = { host: request.host_with_port }
  end
end

#config.action_mailer.default_url_options = { :host => 'mydomain.com' }
$rails console
  User.invite!(email: "ceo@example.com")
ActionView::Template::Error: Missing host to link to! Please provide the :host parameter, set default_url_options[:host], or set :only_path to true
...stacktrace

class ApplicationMailer < ActionMailer::Base
  default from: 'yourmail@gmail.com'
  layout 'mailer'
end

config.action_mailer.default_url_options =
  { :host => 'yourapp.herokuapp.com' }
config.action_mailer.delivery_method = :smtp
config.action_mailer.smtp_settings = {
  address:              'smtp.gmail.com',
  port:                 587,
  domain:               'heroku.com',
  user_name:            'yourmail@gmail.com',
  password:             'yourgmailpassword',
  authentication:       'login',
  enable_starttls_auto: true
}