No, not the Mulder and Scully XFiles, this is the xfilees.biz domain, hosted at Yahoo's AltaVista netblock.
Our dear phisher has made two mistakes here however, firstly, the .htm page attached to the e-mail, as you can see in the screenshot, is not presented properly (they forgot to base ref the HMRC domain, so it's not displayed properly). Secondly, HMRC NEVER sends out attachments such as this, and finally, they didn't bother checking who they're trying to phish - so I got a copy (woops!).
A quick look at the .htm's source code, instantly gives away who is responsible for this particular scam (and don't worry, I've notified HMRC, your hosting company, and of course the authorities);
The domain WhoIs shows little;
Notice the registration date? Yep, it was just created yesterday (aww and you gots blacklisted already?).
Little tip for you guys by the way, the IP block this one is hosted on, is also known for malware and exploits, so may aswell just blackhole it.