Back in September, Microsoft made their preview of the new Outlook app publicly available to people on the preview tracks. This “New Outlook” is known internally at Microsoft as “Project Monarch”. The idea is to try to bring all the various outlook and mail apps on all the different platforms (Windows, macOS, Android, iOS) into a common set of communication protocols known as “hx”.

Well, all of them except for Outlook for Windows, since the MAPI protocol it uses is much richer than anything any of the other platforms are currently using. At least for now. This plan was announced at Ignite (the Microsoft developer conference) a few years back, and little bits of info have leaked to the Internet since then.

Windows Mail in Windows 10 and Windows 11 have already been migrated to the hx stack, and now you have the option to try out “New Outlook” on the Mac, which now uses it too.

When you move to “New Outlook” on Mac, your data gets moved into a new mail database with the filename HxStore.hxd. This is the same file and format that Windows 10 Mail and Windows 11 Mail are already using.

Common is good, right?

Yes, but not if it’s proprietary. The HxStore.hxd format is completely unknown among forensic and eDiscovery apps, and there’s no data about it, anywhere.

Normally, this isn’t a problem, because there are people like us who can dig into new file formats like this new hxstore.hxd format to figure them out and unlock your data, but this file, or at least the latest versions of this file format, are encrypted. This makes it very difficult, if not impossible, to reverse-engineer.

So don’t upgrade to “New Outlook” just yet. If you already have, revert back. There aren’t any tools available yet to repair this file or recover your data — making it a risky place to keep it. For now 😉

The HxStore.hxd file: don’t upgrade to “New Outlook” just yet
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