File this one in the "sources said" folder. But I've now heard from three of my contacts that Microsoft has completed and is testing internally a version of Outlook that runs on Windows RT-based devices.
This "Outlook RT" would run on Microsoft's ARM-based Surface RT devices, as well as any/all other ARM-based Windows RT tablets and PCs.
Here's the catch, though: According to two of these three sources, when/whether Microsoft will make Office RT commercially available is not yet decided. This might not ever happen, these sources stressed.
Again, according to these sources, there's supposedly some internal back-and-forth between different teams as to whether Microsoft should or shouldn't release Outlook RT.
Microsoft currently has its own Mail client for Windows 8 and Windows RT -- a product that is not seen as very robust or solid by many of us Surface RT/Windows RT users. The Windows RT Mail client is not even as good as the Mail client that's part of Windows Phone, many of us feel.