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Use multipart/alternative as content_type of email

05 Aug 2010

Richard Huang (flyerhzm@gmail.com)

Not all the email clients support html format well, we should make our sent emails support both plain text and html format for different email clients.

text/plain

By default Rails sending an email with plain/text content_type, for example

# app/models/notifier.rb
def send_email(email)
  subject       email.subject
  from          email.from
  recipients    email.recipients
  sent_on       Time.now
  body          :email => email
end

# app/views/notifier/send_email.html.erb
Welcome to here: <%= link_to @email.url, @email.url %>

The sent email is a plain text email

Date: Thu, 5 Aug 2010 16:38:07 +0800
From: RailsBP <team@rails-bestpractices.com>
To: flyerhzm@gmail.com
Mime-Version: 1.0
Content-Type: text/plain; charset=utf-8

Welcome: <a href="http://rails-bestpractices.com">http://rails-bestpractices.com</a>

The link url is just displayed as a plain text because of the email content_type.

text/html

If we want the email clients to display link url as html format, we should change the content_type to text/html.

# app/models/notifier.rb
def send_email(email)
  subject          email.subject
  from             email.from
  recipients       email.recipients
  sent_on          Time.now
  content_type     "text/html"
  body             :email => email
end

Now the sent email is a html formatted email

Date: Thu, 5 Aug 2010 17:32:27 +0800
From: RailsBP <team@rails-bestpractices.com>
To: flyerhzm@gmail.com
Mime-Version: 1.0
Content-Type: text/html; charset=utf-8

Welcome: <a href="http://rails-bestpractices.com">http://rails-bestpractices.com</a>

Now the email client can display the link url correctly with html format.

multipart/alternative

But we can't promise that all the email clients support the html format and some users will set the email client to display plain text email instead of html formatted email. How should we do?

We should use multipart/alternative as email content_type to support both text/plain and text/html emails.

# app/models/notifier.rb
def send_email(email)
  subject          email.subject
  from             email.from
  recipients       email.recipients
  sent_on          Time.now
  content_type     "multipart/alternative"

  part :content_type => "text/html",
    :body => render_message("send_email_html", :email => email)

  part "text/plain" do |p|
    p.body = render_message("send_email_plain", :email => email)
    p.transfer_encoding = "base64"
  end
end

# app/views/notifier/send_email_html.erb
# app/views/notifier/send_email_plain.erb

As you see, we can set the email content_type to multipart/alternative, then define content_type text/html render the file app/views/notifier/send_email_html.erb and content_type text/plain render the file app/views/notifier/send_email_plain.erb. So the sent email is as follows

Date: Thu, 5 Aug 2010 16:17:35 +0800
From: RailsBP <team@rails-bestpractices.com>
To: flyerhzm@gmail.com
Mime-Version: 1.0
Content-Type: multipart/alternative; boundary=mimepart_4c5a739f40ca1_967c1a0d6123


--mimepart_4c5a739f40ca1_967c1a0d6123
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: Quoted-printable
Content-Disposition: inline

Welcome: <a href="http://rails-bestpractices.com">http://rails-bestpractices.com</a>

--mimepart_4c5a739f40ca1_967c1a0d6123
Content-Type: text/html; charset=utf-8
Content-Transfer-Encoding: Quoted-printable
Content-Disposition: inline

Welcome: <a href="http://rails-bestpractices.com">http://rails-bestpractices.com</a>

--mimepart_4c5a739f40ca1_967c1a0d6123--

As you see, the content_type of email is multipart/alternative now, and the body of email is divided into two parts, one is for text/plain, the other is for text/html. So email clients can decide which format of email to display.

Convention

It's cool, but can the codes be simpler? Of course, there is a convention to simplifier the multipart/alternative content_type

def send_email(email)
  subject          email.subject
  from             email.from
  recipients       email.recipients
  sent_on          Time.now
  body             :email => email
end

# app/views/notifier/send_email.text.plain.erb
# app/views/notifier/send_email.text.html.erb

Please note the file extensions for notifier send_email method, one is .text.plain.erb, the other is .text.html.erb, they are the email views for text/plain and text/html according to their names. ActionMailer will detect the file extension, if .text.plain and .text.html exist, the content_type of email will be set to multipart/alternative automatically.

Updated: in rails3, the mail view file names should be send_email.html.erb and send_email.text.erb

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