Content Type for MHT files

https://stackoverflow.com/questions/31250

09-06-2019
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Question

What is the content type for MHT files?

Solution

application/octet-stream

You can stream the contents of a .eml file to a browser with this content type and .mht as the extension, and the email will be rendered similar to the way it is rendered in an email client.

OTHER TIPS

Microsoft, who co-authored the spec for MHT, seem to think that it should be 'message/rfc822' on this support page.

No specific MIME type seems to be given in the spec though: RFC2557: MIME Encapsulation of Aggregate Documents, such as HTML (MHTML)

I know this is old, but I thought it should be clarified and explained in more detail...

@Guy Starbuck wrote:

message/rfc822

RFC 822 - STANDARD FOR THE FORMAT OF ARPA INTERNET TEXT MESSAGES

The problem with this answer is that MHTML files are not defined by RFC822.

The correct content-type for MHTML files (.mht, .mhtml) is multipart/related.

As stated above, RFC822 defines the format for internet text messages. The content-type message/rfc822 is used for text attachments within email messages [1][2].

Most of us have probably received a reply to an email where, instead of being quoted inline, the original message is included as an attachment. That attachment has a content-type of message/rfc822. In such emails, the content-types break down as follows:

multipart/mixed = entire message
text/plain = text of reply email
message/rfc822 = original email as attachment

On the other hand, as noted by @feeela, MHTML files are defined in RFC2557. MHTML files are comprised of many different parts, each of which can have a different content-type. However, RFC2557 defines the content-type of the entire file as multipart/related.

[1] RFC1341: MIME (Multipurpose Internet Mail Extensions)
[2] The message Content-Type

message/rfc822

RFC 822 - STANDARD FOR THE FORMAT OF ARPA INTERNET TEXT MESSAGES

Here is a hyperlink: message/rfc822

"MIME Encapsulation of Aggregate Documents, such as HTML" (MHTML or MHT) is an IETF standard proposed in 1999 in the RFC 2557.

Its MIME type is multipart/related and the extension is .mht.