What is the MIME type of .eml files in emails

Question

I want to attach a MTA report (not delivered bounce mail) to an email, but what is the correct MIME type?

I fetch the full body of the MTA report with

$body = imap_fetchbody($this->Mailbox->stream, $this->header->uid, '', FT_UID);

But what is the correct MIME type for attached .eml files?

Have tried message/rfc822 but when you open the file in Thunderbird the popup windows is empty. Have also tried text/plain but then the attachment is opended as plain text. I want to open the attachment .eml as an email

When you receive a MTA report (not delivered) the bounce mail is always forwarded as an attachment

I want to attach the full MTA report + forwarded bounce mail to a new mail

Vineyard

Our (proprietary) mail client at work just sets Content-Type: application/octet-stream; name="xxx.EML" Content-Transfer-Encoding: base64 Content-Disposition: attachment; filename="xxx.EML", and is able to open the received attachment “as” an email again via double click, though I could not say whether that was not probably due to the registered file ending. What happens when you send yourself a mail in Thunderbird, that you just attached an EML file to - does it work as desired then? If so, check the source code of that mail. – Ontario

@CBroe its seems to work with application/octet-stream create an answer :) – Vineyard

Answer 1

Content-Type: application/octet-stream should do the trick.

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Our (proprietary) mail client at work just sets Content-Type: application/octet-stream; name="xxx.EML" Content-Transfer-Encoding: base64 Content-Disposition: attachment; filename="xxx.EML", and is able to open the received attachment “as” an email again via double click. Since that mime type is anything but specific, I suppose it falls back onto the file type handler registered for the .eml suffix on the OS level.

Ontario

This doesn't work for Gmail. When you receive an email with an eml attachment of type application/octet-stream, Gmail's web interface refuses to load it. – Eijkman

Answer 2

message/rfc822, "encapsulated message".

(That string is reported as the Type when an .eml file is dropped in React Dropzone. YMMV.)

Impostor

That's also what the CLI tool mimetype /path/to/file tells me – Aerodyne

I wish this is the selected answer. Email clients are just too flexible on this. application/octet-stream is for a generic file with bytes. – Dorathydorca

This is the right answer – Fritillary

When you get a bounce-back email and the original sent email is contained, the mime type of that original email is message/rfc822 – Cortico

Answer 3

There is no mime type for it based on list as of 2020-12-23. See:

http://www.iana.org/assignments/media-types/media-types.xhtml

Argos