What is an MSG file?

What MSG is

MSG is a binary format, meaningful only to a program that knows it. It is used for email.

The extension is .msg, and the full name is Outlook Message. Both matter less than what the file can hold, which is what the rest of this page is about.

Where MSG came from

Microsoft published it in 1997.

A format that has been readable for that long is a format worth trusting with something you want back in ten years.

The specification is published, but by its owner

It is written down and implementable, though the vendor decides what the next version looks like. In practice that is enough for the file to keep opening; it is not enough to be sure of it.

What opens MSG

Microsoft Outlook reads it, and so do most programs of the same kind.

If a file will not open, the format is rarely the problem — it is more often that the program predates it. Converting to something older is the reliable way past that, and it is what the rest of this site is for.

Opening it in a browser

No browser reads it.

That is the single most common reason to convert it: not that the format is bad, but that the place you want to show the file cannot read it.

It is a delivery format

MSG is meant to be handed over rather than worked in. Editing one is possible and rarely pleasant; the sane approach is to change the source and export again.

What goes wrong with it

The recurring complaints: support outside its home ground is uneven.

None of these is a reason to avoid the format. They are the things worth knowing before you are surprised by one, which is a different claim and a more useful one.

The facts, in one place

Formats worth considering instead of MSG

• Email Message
• Portable Document Format