Inline Attachments for ActionMailer

ActionMailer’s support for inline attachments sucks. Totally. Until now.

If you have ever tried to get an inline attachment working in Rails 2.x or even Rails 3 more recently, you were faced with an uphill battle that really did not deserve to be there.

For those not in the know, an Inline attachment in an email is simply an attachment that has a Content-Disposition of “inline” and allows you to reference it by using an HTML image tag with its source attribute pointing to cid:conent-id-of-image-part.

This allows you to put logos in your emails, header images etc. All embedded within the email itself.

So enough talk, this is how you do it, say you have a welcome message in your Action Mailer class, and in this welcome message you want to embed your company logo, which is conveniently located in your Rails root “public/images” directory.

First in your mailer, you would do:

class Notifier < ActionMailer::Base

  def welcome
    data = File.read(Rails.root.join('public/images/logo.png'))
    attachments.inline['logo.png'] = data
    mail
  end

end

Notice the [inline]{.underline} call to attachments? What this does is tells Mail to mark this file with a content disposition of “inline” instead of the usual “attachment”.

Then in your view you would do:

<h1>Thank you for choosing ErnCorp!</h1>
<p><%= image_tag attachments['logo.png'].url -%></p>

Here, we are just interrogating the mail.attachments hash for the attachment with the filename “logo.png” and then calling [url]{.underline} on the attachment we fine. This generates a standard email content ID resource locator (cid tag) that looks something like: cid:4c0da20e13de6@mikel.local.mail

And that is it!

Now the cool thing about this is that when you send this email, ActionMailer looks through your attachments list finding any inline attachments, if it finds some, then it changes your email to a multipart/related content type and then makes these attachments available to the view through the attachments helper.

Anyway, this is now pushed. Enjoy and have fun!

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