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Sending Emails with Ruby

Let’s say you have a working Ruby app and need to add an email delivery functionality to it. This could be related to user authentication, or any other kind of transactional emails, it makes no difference. This tutorial is tailored is aimed at helping you implement sending emails with Ruby.

If you want to read the full article, check it out the on the Mailtrap’s blog: Sending Emails with Ruby

Options for sending an email in Ruby

Mostly, you can pick one of the three options.

The simplest one is using Net::SMTP class. It provides the functionality to send email via SMTP. The drawback of this option is that Net::SMTP lacks functions to compose emails. You can always create them yourself, but this takes time.

The second option is to use a dedicated Ruby gem like Mail, Pony, or others. These solutions let you handle email activities in a simple and effective way. Action Mailer is a perfect email solution through the prism of Rails. And, most likely, this will be your choice.

The third option is class Socket. Mostly, this class allows you to set communication between processes or within a process. So, email sending can be implemented with it as well. However, the truth is that Socket does not provide you with extensive functionalities, and you’re unlikely to want to go with it.

Now, let’s try to send an email using each of the described solutions.

How to send emails in Ruby via Net::SMTP

From our experience, the use of that option in a regular web app is uncommon. However, sending emails via Net::SMTP could be a fit if you use mruby (a lightweight implementation of the Ruby language) on some IoT device. Also, it will do if used in serverless computing, for example, AWS Lambda. Check out this script example first and then we’ll go through it in detail.

require 'net/smtp'

message = <<END_OF_MESSAGE
From: YourRubyApp <info@yourrubyapp.com>
To: BestUserEver <your@bestuserever.com>
Subject: Any email subject you want
Date: Tue, 02 Jul 2019 15:00:34 +0800

Lorem Ipsum
END_OF_MESSAGE
Net::SMTP.start('your.smtp.server', 25) do |smtp|
  smtp.send_message message,
  'info@yourrubyapp.com',
  'your@bestuserever.com'
end
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This is a simple example of sending a textual email via SMTP (official documentation can be found here). You can see four headers: From, To, Subject, and Date. Keep in mind that you have to separate them with a blank line from the email body text. Equally important is to connect to the SMTP server.

Net::SMTP.start('your.smtp.server', 25) do |smtp|

Naturally, here will appear your data instead of ‘your.smtp.server‘, and 25 is a default port number. If needed, you can specify other details like username, password, or authentication scheme (:plain, :login, and :cram_md5). It may look as follows:

Net::SMTP.start('your.smtp.server', 25, ‘localhost’, ‘username’, ‘password’ :plain) do |smtp|

Here, you will connect to the SMTP server using a username and password in plain text format, and the client’s hostname will be identified as localhost.

After that, you can use the send_message method and specify the addresses of the sender and the recipient as parameters. The block form of SMTP.start (Net::SMTP.start('your.smtp.server', 25) do |smtp|) closes the SMTP session automatically.

In the Ruby Cookbook, sending emails with the Net::SMTP library is referred to as minimalism since you have to build the email string manually. Nevertheless, it’s not as hopeless as you may think of. Let’s see how you can enhance your email with HTML content and even add an attachment.

Sending an HTML email in Net::SMTP

Check out this script example that refers to the message section.

message = <<END_OF_MESSAGE
From: YourRubyApp <info@yourrubyapp.com>
To: BestUserEver <your@bestuserever.com>
MIME-Version: 1.0
Content-type: text/html
Subject: Any email subject you want
Date: Tue, 02 Jul 2019 15:00:34 +0800

A bit of plain text.

<strong>The beginning of your HTML content.</strong>
<h1>And some headline, as well.</h1>
END_OF_MESSAGE

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Apart from HTML tags in the message body, we’ve got two additional headers: MIME-Version and Content-type. MIME refers to Multipurpose Internet Mail Extensions. It is an extension to Internet email protocol that allows you to combine different content types in a single message body. The value of MIME-Version is typically 1.0. It indicates that a message is MIME-formatted.

As for the Content-type header, everything is clear. In our case, we have two types – HTML and plain text. Also, make sure to separate these content types using defining boundaries.

Except for MIME-Version and Content-type, you can use other MIME headers:

  • Content-Disposition – specifies the presentation style (inline or attachment)
  • Content-Transfer-Encoding – indicates a binary-to-text encoding scheme (7bit, quoted-printable, base64, 8bit, or binary).

Sending an email with an attachment in Net::SMTP

Let’s add an attachment, such as a PDF file. In this case, we need to update Content-type to multipart/mixed. Also, use the pack("m") function to encode the attached file with base64 encoding.

require 'net/smtp'

filename = "/tmp/Attachment.pdf"
file_content = File.read(filename)
encoded_content = [file_content].pack("m")   # base64

marker = "AUNIQUEMARKER"
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After that, you need to define three parts of your email.

Part 1 – Main headers

part1 = <<END_OF_MESSAGE
From: YourRubyApp <info@yourrubyapp.com>
To: BestUserEver <your@bestuserever.com>
Subject: Adding attachment to email
MIME-Version: 1.0
Content-Type: multipart/mixed; boundary = #{marker}
--#{marker}
END_OF_MESSAGE
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Part 2 – Message action

part2 = <<END_OF_MESSAGE
Content-Type: text/html
Content-Transfer-Encoding:8bit

A bit of plain text.

<strong>The beginning of your HTML content.</strong>
<h1>And some headline, as well.</h1>
--#{marker}
END_OF_MESSAGE
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Part 3 – Attachment

part3 = <<END_OF_MESSAGE
Content-Type: multipart/mixed; name = "#{filename}"
Content-Transfer-Encoding:base64
Content-Disposition: attachment; filename = "#{filename}"

#{encoded_content}
--#{marker}--
END_OF_MESSAGE
Now, we can put all the parts together and finalize the script. That’s how it will look:
require 'net/smtp'

filename = "/tmp/Attachment.pdf"
file_content = File.read(filename)
encoded_content = [file_content].pack("m")   # base64

marker = "AUNIQUEMARKER"

part1 = <<END_OF_MESSAGE
From: YourRubyApp <info@yourrubyapp.com>
To: BestUserEver <your@bestuserever.com>
Subject: Adding attachment to email
MIME-Version: 1.0
Content-Type: multipart/mixed; boundary = #{marker}
--#{marker}
END_OF_MESSAGE

part2 = <<END_OF_MESSAGE
Content-Type: text/html
Content-Transfer-Encoding:8bit

A bit of plain text.

<strong>The beginning of your HTML content.</strong>
<h1>And some headline, as well.</h1>
--#{marker}
END_OF_MESSAGE

part3 = <<END_OF_MESSAGE
Content-Type: multipart/mixed; name = "#{filename}"
Content-Transfer-Encoding:base64
Content-Disposition: attachment; filename = "#{filename}"

#{encoded_content}
--#{marker}--
END_OF_MESSAGE

message = part1 + part2 + part3

begin
  Net::SMTP.start('your.smtp.server', 25) do |smtp|
    smtp.send_message message,
    'info@yourrubyapp.com',
    'your@bestuserever.com'
  end
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Can I send an email to multiple recipients in Net::SMTP?

Definitely, you can. send_message expects second and subsequent arguments to contain recipients’ emails. For example, like this:

Net::SMTP.start('your.smtp.server', 25) do |smtp|
  smtp.send_message message,
  'info@yourrubyapp.com',
  'your@bestuserever1.com',
  ‘your@bestuserever2.com’,
  ‘your@bestuserever3.com
end

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Best Ruby gems for sending emails

In Ruby ecosystem, you can find specific email gems that can improve your email sending experience.

Ruby Mail

This library is aimed at giving a single point of access to manage all email-related activities including sending and receiving email.

Pony

You might have heard a fairy tale about sending an email in one command. Hold on to your hats, cause it’s real and provided by Pony gem.

ActionMailer

This is the most popular gem for sending emails on Rails. In case your app is written on top of it, ActionMailer will certainly come up. It lets you send emails using mailer classes and views.

Using Mailtrap to test email sending with Net::SMTP

Setup is very simple. Once you’re in your demo inbox, copy the SMTP credentials on the SMTP Settings tab and insert them in your code. Or you can get a ready-to-use template of a simple message in the Integrations section. Just choose a programming language or framework your app is built with.

require 'net/smtp'

message = <<END_OF_MESSAGE
From: YourRubyApp <info@yourrubyapp.com>
To: BestUserEver <your@bestuserever.com>
Subject: Any email subject you want
Date: Tue, 02 Jul 2019 15:00:34 +0800

Lorem Ipsum
END_OF_MESSAGE
Net::SMTP.start('smtp.mailtrap.io', 587, '<username>', '<password>', :cram_md5) do |smtp|
  smtp.send_message message,
  'info@yourrubyapp.com',
  'your@bestuserever.com'
end
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If everything is alright, you’ll see your message in the Mailtrap Demo inbox. Also, you can try to check your email with HTML content and an attachment. Mailtrap allows you to see how your email will look and check HTML if necessary.

Create a Mailtrap account and try to test it on your own for free!

You have just read the full tutorial on how to test and send emails in Ruby. There is still a lot to check out when it comes to Ruby Mail, Pony and Action Mailer. Learn more about Ruby Gems & Socket Class in our full Sending Emails with Ruby article at Mailtrap.io.

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