Altoros is a big data and Platform-as-a-Service specialist that provides system integration for IaaS/cloud providers, software companies, and information-driven enterprises. Areas of expertise include Cloud Foundry, Hadoop, and NoSQL solutions, as well as Microsoft .NET, Java, Ruby on Rails, and mobile technologies.

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This post contains some notes regarding different aspects of work with email in Ruby on Rails and covers such topics as sending and receiving email as well as using address tagging.

Sending email

Sending email in Rails is being performed with the use of the ActionMailer::Base class. You can check the docs to get more details.


It appears to be convenient to configure ActionMailer in different ways for different environments.


A great tool for this environment is the Letter Opener gem. It intercepts all outgoing email and opens each email in a separate tab of your default browser instead of real sending. Using it allows you not to worry about sending unwanted emails by accident to your real users mailboxes and not to bother you customer and testers during development or debugging some mailer. Here is an example of ActionMailer config for development environment:

# config/environments/development.rb

config.action_mailer.perform_deliveries = true config.action_mailer.raise_delivery_errors = true config.action_mailer.delivery_method = :letter_opener config.action_mailer.default_url_options = { host: ‘localhost:3000’, protocol: ‘http’ }

Another option is to use the MailCatcher gem which is also great but Letter Opener is just simpler so I prefer using it.


It’s rather common to have a 3-environments infrastructure - development, staging and production. Staging environment is usually being used for testing features to work properly (by testers and/or customer) before releasing them to production. In this case it’s important for a tester to be able to verify that some email is being sent successfully and is implemented correctly. At the same time emails should not be sent to real users. In this case Letter Opener is not an option. MailCatcher would be suitable here but again there is a simpler and more convenient option - Mailtrap. You can register a basic account (which is pretty sufficient in most of cases) for free. With this approach email delivery is being actually performed but to mailbox instead of end user mailboxes. Also as it is expected Mailtrap provides a web interface to manage sent emails. Below is an example of ActionMailer config for staging environment:

# config/environments/staging.rb

config.action_mailer.perform_deliveries = true config.action_mailer.raise_delivery_errors = false config.action_mailer.delivery_method = :smtp config.action_mailer.smtp_settings = { user_name: ‘examplecom-staging-g8257th95725e9k1’, password: ‘mypassword’, address: ‘’, port: ‘2525’, authentication: :plain, } config.action_mailer.default_url_options = { host: ‘’, protocol: ‘http’ }


In this environment everything is pretty obvious as you should have ActionMailer to be configured for real email delivery to your users. ActionMailer config example for production environment:

# config/environments/development.rb

config.action_mailer.perform_deliveries = true config.action_mailer.raise_delivery_errors = false config.action_mailer.delivery_method = :smtp config.action_mailer.smtp_settings = { address: ‘’, domain: ‘’, user_name: ‘myusername’, password: ‘mypassword’, authentication: :plain, enable_starttls_auto: true, port: 587, } config.action_mailer.default_url_options = { host: ‘’, protocol: ‘http’ }

By the way if anyone uses Gmail for sending email here is an example of smtp settings for it:

config.action_mailer.smtp_settings = {
  address: ‘’,
  domain: ‘’,
  password: ‘mypassword’,
  authentication: :plain,
  enable_starttls_auto: true,
  port: 587,


Instead of inheriting your mailers directly from ActionMailer::Base it is convenient to create a parent ApplicationMailer mailer class where you can configure default mailer properties as for example layout and “from”. Later you create your mailers inherited from it.

# app/mailers/application_mailer.rb

class ApplicationMailer < ActionMailer::Base

layout ‘application_mailer’ default from:


Having a layout provides you with obvious advantages of DRYing your email views (for example you can easily add shared header and footer).

/ app/views/layouts/application_mailer.html.haml

    %meta{‘http-equiv’ => “Content-Type”, content: “text/html; charset=UTF-8”}
    = render ‘shared/email_header’
    = yield
    = render ‘shared/email_footer’

Custom mailer

So, let’s suppose that your application provides users with a capability to send in-site messages to each other with an option to send an email to the recipient user as well (via a checkbox or something). A possible simplified create action responding to js format for this could look something like this:

# app/controllers/messages_controller.rb

class MessagesController < ApplicationController

def create @recipient = User.find(params[:recipient_id]) @message = if MessageMailer.new_message(@message, recipient).deliver else # some error processing end end


By the way for performance and usability reasons it is better to send emails asynchronously, for example using Sidekiq gem. In this case your code would look like this:

MessageMailer.delay.new_message(@message, recipient)

Ok, let’s look at our MessageMailer.

# app/mailers/message_mailer.rb

class MessageMailer < ApplicationMailer

def new_message(message, recipient) @message = message mail({ subject: message.subject, to:, }) end


And we should have a corresponding view:

/ app/views/message_mailer/new_message.html.haml

%h2= @message.subject
%p= simple_format @message.content

And that is all. Basic email should now be sent after invoking the “create” action of MessagesController.

Pretty “From” field

Let’s modify a bit From field of the email in order to clearly see who sent you a message when you receive such email. And also let’s not show the actual user email address (let’s assume it is for private reasons) but instead we’ll use the email address which we set as the default in the ApplicationMailer class.

  from: #{} <#{default_params[:from]}>”,
  subject: message.subject,

Assuming a message was sent by John Doe for example Gmail will show an email sent this way as from “John Doe”. Many email clients will show it as from “John Doe \<>”. I think it looks much better than just from “” and besides it allows you to search for emails based on their actual sender.


Suppose we want to send some file attachments along with an email. File uploads are out of scope of this post so let’s just assume that we have following models:

class Message < ActiveRecord::Base
  has_many :content_files
  belongs_to :author, class_name: ‘User’, foreign_key: ‘created_by’

class ContentFile < ActiveRecord::Base
  mount_uploader :attachment, ContentFileUploader
  belongs_to :message

Here the ContentFile model has a mounted as :attachment CarrierWave uploader (yep, I prefer to use CarrierWave for file uploads).

Also you should keep in mind that you can’t send an arbitrary amount of data in attachments as it’s most likely that email size will be limited at the destination mailserver. For example current Gmail total email size limit (including body and attachments) is equal to 25 MB. So we should process attachments somehow taking into account their size. There are plenty of options that you could implement including blocking messages with attachments size overlimit from being sent at all, but to my mind a better solution is to send just as much data as possible and if there are attachments that were not sent then for example explicitly tell about it to the recipient user and invite him to see an original message at your website. Code responsible for this could be as follows:

class MessageMailer < ApplicationMailer

def new_message(message, recipient) @message = message

<span class="n">total_attachments_size</span> <span class="o">=</span> <span class="mi">0</span>
<span class="n">message</span><span class="p">.</span><span class="nf">content_files</span><span class="p">.</span><span class="nf">each</span> <span class="k">do</span> <span class="o">|</span><span class="n">content_file</span><span class="o">|</span>
  <span class="k">next</span> <span class="k">if</span> <span class="n">total_attachments_size</span> <span class="o">+</span> <span class="n">content_file</span><span class="p">.</span><span class="nf">filesize</span> <span class="o">&gt;=</span> <span class="no">Message</span><span class="o">::</span><span class="no">MAX_ATTACHMENTS_TOTAL_SIZE</span>
  <span class="n">attachments</span><span class="p">[</span><span class="n">content_file</span><span class="p">.</span><span class="nf">title</span><span class="p">]</span> <span class="o">=</span> <span class="no">File</span><span class="p">.</span><span class="nf">read</span><span class="p">(</span><span class="n">content_file</span><span class="p">.</span><span class="nf">attachment</span><span class="p">.</span><span class="nf">file</span><span class="p">.</span><span class="nf">path</span><span class="p">)</span>
  <span class="n">total_attachments_size</span> <span class="o">+=</span> <span class="n">content_file</span><span class="p">.</span><span class="nf">filesize</span>
<span class="k">end</span>

<span class="n">mail</span><span class="p">({</span>
  <span class="ss">from: </span><span class="s2">"</span><span class="si">#{</span><span class="n">message</span><span class="p">.</span><span class="nf">author</span><span class="p">.</span><span class="nf">full_name</span><span class="si">}</span><span class="s2"> &lt;</span><span class="si">#{</span><span class="n">default_params</span><span class="p">[</span><span class="ss">:from</span><span class="p">]</span><span class="si">}</span><span class="s2">&gt;"</span><span class="p">,</span>
  <span class="ss">subject: </span><span class="n">message</span><span class="p">.</span><span class="nf">subject</span><span class="p">,</span>
  <span class="ss">to: </span><span class="n">recipient</span><span class="p">.</span><span class="nf">email</span><span class="p">,</span>
<span class="p">})</span>



The algorithm above of course is not the most perfect one and can be improved in many ways depending on your needs. This implementation tries first to create attachments based on first uploaded files assuming that they are the most important and then it tries to add as many files as possible up to the provided limit skipping large files causing overlimit.

Regarding content_file.filesize - I usually store filesize in the database for faster access to it and to avoid additional disk operations.

Great, now we can send emails with attachments. Next let’s see how to receive mail in Rails.

Receiving email

Without any doubts it would be very useful to not only send emails but also to receive them and process in the context of your Rails application. The most common solution for this task is to use the Mailman gem. Setting up Mailman is pretty simple. Let’s see how to configure it to fetch email from a Gmail account. First, add it to your Gemfile

gem ‘mailman’, require: false

and run bundle install. Next let’s create a file which we will use to run mailman as a background process.

# script/mailman_daemon

#!/usr/bin/env ruby require ‘daemons’‘script/mailman_server’)

We will be able to run it almost as a standard UNIX daemon:

bundle exec script/mailman_daemon start|stop|restart|status

Next let’s create the actual Mailman server script. Here is an example of what it could look like:

#!/usr/bin/env ruby
require “mailman”

Mailman.config.logger =“../../log/mailman.log”, FILE)) Mailman.config.poll_interval = 60 Mailman.config.pop3 = { server: ‘’, port: 995, ssl: true, username:, password: ‘mypassword’, } do to ‘’ do # at this point we have “message” and “params” methods available # so you can check fetched message and params. Everything before the “@” character # will be available as params[:folder] message.inspect params.inspect end

default do # this is a catch-all route end end

Here we configured Mailman to get email from a Gmail account via the POP3 protocol once a minute. Within a block we define rules to determine how to process an email in a way very similar to the Rails router approach - you define routes one by one and the first suitable route’s block will be executed. Pretty simple, isn’t it? Great, now you can both send and receive email in Rails.

Address tags

Another very important and useful technique anyone should be familiar with is “address tagging” which is sometimes referenced as “sub-addressing” (eg. in RFC 5233). The point of this technique is that you can provide some additional info when you send an email right in an email address after a certain separator (usually a + character) this way - All emails sent to this address will be actually delivered to address.

One of the most well-known use cases of this technique is to determine sites whose database was stolen (or sold, who knows). So imagine that you have an email address and you want to register at some site During registration provide your email as If after some time period you start receiving magic pills advertising emails with To header field equal to then it’s pretty obvious where those spammers got your email. Sometimes sites can have email validation rules that will reject your email address containing + or some other characters.

Also you should keep in mind that this technique can’t be used in some cases because not all mail servers support it or have it enabled by default (eg. Gmail supports it). So if you’re setting up your own mail server then you better check the docs to be sure.

Rails + Mailman + Address tagging

A very interesting functionality can be achieved combining all the above described techniques. Imagine you have a website where users can send messages to each other and you also automatically send a copy of a message by email (or users can manually choose to send a copy to email) - pretty standard feature. It would be great if a recipient user could reply to your email right in his (or her) email client. Let’s see how we can do it. Further I provide a pseudo code which can lack some details but is sufficient to get the idea.

Let’s suppose we have following models:

class User < ActiveRecord::Base

class MessageDelivery < ActiveRecord::Base
  belongs_to :recipient, class_name: “User”, foreign_key: “recipient_id”
  belongs_to :message

class Message < ActiveRecord::Base
  belongs_to :author, class_name: “User”, foreign_key: “author_id”
  has_many :message_deliveries
  has_many :recipients, through: :message_deliveries

and a MessagesController controller with create action responsible for sending messages which looks like this:

class MessagesController < ApplicationController

def create @message = if @message.recipients.each do |recipient| # as I mentioned previously it’s strongly recommended to process email sending in background MessageMailer.delay.email_copy(@message, recipient) end else # some error processing end end


Our mailer class MessageMailer could look like this:

class ApplicationMailer < ActionMailer::Base
  layout ‘application_mailer’
  default from:

class MessageMailer < ApplicationMailer

def email_copy(message, recipient, options = {}) @message = message mail({ from: #{} <#{default_params[:from]}>”, subject: “New message”, to:, reply_to: default_params[:from].gsub(‘@’, “+f-#{recipient.uuid}-t-#{}-m-#{@message.uuid}@”), }) end


Here I set Reply-to field to contain our default From email address but with addition of some useful information using address tagging. What it gives is that an user will still receive emails from address, but when he hits “Reply” in his email client than the To email address will be equal to the one we passed in Reply-to field. Of course we make an assumption that an user will not change it, but I think that in most of cases he indeed will not.

To my mind it’s better to send some hashed values rather than just plain ids as the system will be more resistant to fraud actions in this case. Also it’s better to use one-time hashes and expire them after a message is received.

Mailman route for catching these emails can look like this: do
  to ‘f-%from_uuid%-t-%to_uuid%-m-%message_uuid%@’ do
    # here you can load all records that you need
    from_user = User.find_by_uuid(params[:from_uuid])
    to_user = User.find_by_uuid(params[:to_uuid])
    original_message = Message.find_by_uuid(params[:message_uuid])
    # and perform some processing
    # remember that at this point you have access to a Mailman “message” method which returns Mailman message object - you can get all details of the incoming email from it

In Mailman you can create a new reply-message and also send it’s copy by email. This way you’ll implement such a system where users can exchange messages with each other directly from their email clients and in the meantime there will be created messages on your site.

As a bonus you’ll get the capability to collect user’s alternative emails. Some users can have email forwarding enabled in their mailboxes so the actual reply can come from email address that is not present in your database. It allows you to implement users sign in based on alternative emails too apart from the one that an user provided during a registration.

Also you should notice that if you have to put some users in CC or BCC fields then you will not be able to recognize an user who used an alternative email to reply to your message. It will happen because you will be able only to put author’s uuid to email Reply-to address and putting recipient’s uuid will not be possible due to there can be a lot of CC-recipients and it just will not make sense. So when an user will use an alternative email you will just not have it in the database. In this case you’ll have to determine who sent a reply message only based on “From” field of the incoming email.

Ok, at this point I’m stopping. I hope this post was useful for you. Thanks for reading!