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.MHTML·File Extension

MHTML Other — A .mhtml file is a MHTML Other. It is a file format typically read and written by specialized applications.

Othermessage/rfc822Compressible

Quick facts

Extension.mhtml

File typeMHTML Other

MIME typemessage/rfc822

CategoryOther

Charset—

CompressibleYes

What is .mhtml

What is a .mhtml file?

A .mhtml file is a MHTML Other. It is a file format typically read and written by specialized applications.

In the mime-db registry it maps to message/rfc822, and it is marked as compressible. When serving .mhtml over HTTP, set the Content-Type header as shown in Developer info below.

Related entities: it maps to message/rfc822 — and is delivered over HTTP via the Content-Type header.

How to open .mhtml files

Use VS Code or xxd to open and edit .mhtml files.
Any text editor (Notepad, VS Code) can inspect the raw content as text.

Developer info

When served over HTTP, responses should set the following header:

Content-Type: message/rfc822

Common software that reads/writes .mhtml:

VS Codexxd7-Zip

Relation chain

.mhtmlextension of

format

MHTML Otherserved as

mime type

message/rfc822sent via header

http header

Related extensions

Related MIME types

Common uses

Application-specific data

How to edit .mhtml files

Open the file with VS Code, make your changes and save.
Most editors preserve the original formatting and encoding — avoid changing the charset.

How to create .mhtml files

Create a new file and save it with the .mhtml extension, or export this format from VS Code.

Frequently asked questions

What programs can open .mhtml files?

Common options include VS Code, xxd, 7-Zip. You can also open many of these files with built-in viewers or a browser.

How do I create a .mhtml file?

Create a new file in any text editor or the app that owns the format and save it with the .mhtml extension.

What is the relationship between .mhtml and the message/rfc822 MIME type?

message/rfc822 is the media type identifier used for .mhtml files during network transfer (for example in the HTTP Content-Type header).

Sources & standards

Updated 2026-09-13

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