Problem sending multipart mail using ActionMailer

I suspect the issue is you're defining the overall email as multipart/alternative, suggesting each part is just an alternate view of the same message.

I use something like the following to send mixed html/plain emails with attachments, and it seems to work OK.

class InvoiceMailer < ActionMailer::Base

  def invoice(invoice)
    from          CONFIG[:email]
    recipients    invoice.email
    subject       "Bevestiging Inschrijving #{invoice.course.name}"
    content_type  "multipart/mixed"

    part(:content_type => "multipart/alternative") do |p|
      p.part "text/html" do |p|
        p.body = render_message 'invoice_html', :invoice => invoice
      end

      p.part "text/plain" do |p|
        p.body = render_message 'invoice_plain', :invoice => invoice
      end
    end

    pdf = Prawn::Document.new(:page_size => 'A4')
    PDFRenderer.render_invoice(pdf, invoice)
    attachment :content_type => "application/pdf", :body => pdf.render, :filename => "factuur.pdf"

    invoice.course.course_files.each do |file|
      attachment :content_type => file.content_type, :body => File.read(file.full_path), :filename => file.filename
    end
  end

end

@jcoleman is correct but if you don't want to use his gem then this may be a better solution:

class MyEmailerClass < ActionMailer::Base
  def my_email_method(address, attachment, logo)

    # Add inline attachments first so views can reference them
    attachments.inline['logo.png'] = logo

    # Call mail as per normal but keep a reference to it
    mixed = mail(:to => address) do |format|
      format.html
      format.text
    end

    # All the message parts from above will be nested into a new 'multipart/related'
    mixed.add_part(Mail::Part.new do
      content_type 'multipart/related'
      mixed.parts.delete_if { |p| add_part p }
    end)
    # Set the message content-type to be 'multipart/mixed'
    mixed.content_type 'multipart/mixed'
    mixed.header['content-type'].parameters[:boundary] = mixed.body.boundary

    # Continue adding attachments normally
    attachments['attachment.pdf'] = attachment
  end
end

This code begins by creating the following MIME hierarchy:

• multipart/related
  • multipart/alternative
    • text/html
    • text/plain
  • image/png

After the call to mail we create a new multipart/related part and add the children of the existing part (removing them as we go). Then we force the Content-Type to be multipart/mixed and continue adding attachments, with the resulting MIME hierarchy:

• multipart/mixed
  • multipart/related
    • multipart/alternative
      • text/html
      • text/plain
    • image/png
  • application/pdf

A nod to James on this, as it helped me get our mailer working right.

A slight refinement to this: First, we use the block arguments within the blocks to add parts (I had problems when I didn't).

Also, if you want to use layouts, you have to use #render directly. Here's an example of both principles at work. As shown above, you need to make sure you keep the html part last.

  def message_with_attachment_and_layout( options )
    from options[:from]
    recipients options[:to]
    subject options[:subject]
    content_type    "multipart/mixed"
    part :content_type => 'multipart/alternative' do |copy|
      copy.part :content_type => 'text/plain' do |plain|
        plain.body = render( :file => "#{options[:render]}.text.plain", 
          :layout => 'email', :body => options )
      end
      copy.part :content_type => 'text/html' do |html|
        html.body = render( :file => "#{options[:render]}.text.html", 
          :layout => 'email', :body => options )
      end
    end
    attachment :content_type => "application/pdf", 
      :filename => options[:attachment][:filename],
      :body => File.read( options[:attachment][:path] + '.pdf' )
  end

This example uses an options hash to create a generic multipart message with both attachments and layout, which you would use like this:

TestMailer.deliver_message_with_attachment_and_layout( 
  :from => '[email protected]', :to => '[email protected]', 
  :subject => 'test', :render => 'test', 
  :attachment => { :filename => 'A Nice PDF', 
    :path => 'path/to/some/nice/pdf' } )

(We don't actually do this: it's nicer to have each mailer fill in a lot of these details for you, but I thought it would make it easier to understand the code.)

Hope that helps. Best of luck.

Regards, Dan