How to send emails with multiple, dynamic smtp using Actionmailer/Ruby on Rails

Question

I saw this post but mine is slightly different:

Rails ActionMailer with multiple SMTP servers

I am allowing the users to send mail using their own SMTP credentials so it actually does come from them.

But they will be sent from the Rails app, so that means for each user I need to send their emails using their own SMTP server.

How can I do that?

Answer 1

Doing what is described in the other answer is not safe; you are setting class variables here, not instanced variables. If your Rails container is forking, you can do this, but now your application is depending on an implementation detail of the container. If you're not forking a new Ruby process, then you can have a race condition here.

You should have a model that is extending ActionMailer::Base, and when you call a method, it will return a Mail::Message object. That is your instance object and is where you should change your settings. The settings are also just a hash, so you can inline it.

msg = MyMailer.some_message
msg.delivery_method.settings.merge!(@user.mail_settings)
msg.deliver

Where in the above mail_settings returns some hash with appropriate keys IE

{:user_name=>username, :password=>password}

Answer 2

Here is a solution that I came up with based on the previous answers and comments. This uses an ActionMailer interceptor class.

class UserMailer < ActionMailer::Base
  default from: proc{ @user.mail_settings[:from_address] }      

  class DynamicSettingsInterceptor
     def self.delivering_email(message)
       message.delivery_method.settings.merge!(@user.mail_settings)
     end
   end
   register_interceptor DynamicSettingsInterceptor
end

Answer 3

For Rails 3.2.x

You can include AbstractController::Callbacks in your mailer class and the do a "after_filter :set_delivery_options" inside the mailer.

The set_delivery_options method would have access to instance variables setup by you in your mailer action and you can access the mail object as "message".

class MyNailer < ActionMailer::Base
  include AbstractController::Callbacks
  after_filter :set_delivery_options

  def nail_it(user)
    @user = user
    mail :subject => "you nailed it"
  end

  private

  def set_delivery_options
    message.delivery_method.settings.merge!(@user.company.smtp_creds)
  end
end

Answer 4

Since Rails 4+ it works to give the credentials directly via the delivery_method_options parameter:

class UserMailer < ApplicationMailer
  def welcome_email
    @user = params[:user]
    @url  = user_url(@user)
    delivery_options = { user_name: params[:company].smtp_user,
                         password: params[:company].smtp_password,
                         address: params[:company].smtp_host }
    mail(to: @user.email,
         subject: "Please see the Terms and Conditions attached",
         delivery_method_options: delivery_options)
  end
end

See Sending Emails with Dynamic Delivery Options (Rails Guides)