MHT Other — A .mht file is a MHT Other. It is a file format typically read and written by specialized applications.
Quick facts
What is .mht
A .mht file is a MHT 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 .mht 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 .mht files
Developer info
When served over HTTP, responses should set the following header:
Content-Type: message/rfc822
Common software that reads/writes .mht:
Relation chain
Related extensions
Related MIME types
Common uses
How to edit .mht files
How to create .mht files
Frequently asked questions
Common options include VS Code, xxd, 7-Zip. You can also open many of these files with built-in viewers or a browser.
Create a new file in any text editor or the app that owns the format and save it with the .mht extension.
message/rfc822 is the media type identifier used for .mht files during network transfer (for example in the HTTP Content-Type header).
Sources & standards
Updated 2026-08-18
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