将邮件消息附加到 Rails 中的邮件

Question

In a Rails 5.1 ActionMailer, I want to attach a Mail object to an e-mail:

def attach_mail(original_email)
  attachments['original-email.eml'] = { mime_type: 'message/rfc822', encoding: '7bit', content: original_email.to_s }
  mail to: 'postmaster', subject: 'mail should be attached'
end

However, this does not produce valid e-mails. Thunderbird lists the attachment with size '0'. Horde lists the attachment with correct size, but does not recognize it as an e-mail.

I've tried variations of the attachments line:

attachments['original-email.eml'] = original_email
attachments['original-email.eml'] = { content: original_email.to_s }
attachments['original-email.eml'] = { mime_type: 'message/rfc822', content: original_email.to_s }

but none of these result in an e-mail with an e-mail attachment.

What's the solution?

Answer 1

Finally figured it out.

To attach an email (Mail object from the 'mail' gem) to an ActionMailer message, you need to specify the MIME type and encoding like so:

def attach_mail(original_email)
  attachments['original-email.eml'] = { mime_type: 'message/rfc822', 
    encoding: '7bit',
    content: original_email.to_s }
  mail to: 'postmaster', subject: 'mail should be attached'
end

This creates a multipart/mixed message which is properly displayed in MUAs.

However, if you happen to add any inline attachment (eg to display a logo image in the ActionMailer e-mail body), the entire message will have a multipart/related mime type. The MUAs that I tried were unable to interpret a multipart/related message with an e-mail attachment.

Therefore, refrain from adding any inline attachments when attaching an e-mail to an e-mail.