Guys, I don't believe that this is legit for a few reasons. As already said, the domain was already down before the email was even sent. A legit company would have noticed this or they are truly incompetent in what they are doing.
"to deactivate the domain name within three (3) working days from your receipt of this notice in order to prevent further action taken against you and your company."
Persoanlly I believe some scammers want the expired domain because they believe it has some value, that's all. They can fake where the email comes from, they can even fake the signature, as a developer I know how this can be done. The server the email was sent from is related to namecheap and namecheap isn't exactly a registrar huge companies go for. It's a highly used registrar by blackhatters, scammers and so on.
They even attached a document which is signed by "legal counsel Jingping Dong". I mean, that name sounds way to funny to be legit and could be found on the web easily.
They haven't even contacted the hosting where the domain was on before even if it's super easy to trace it back what has way more success on a takedown than sending out some email to a random whois protection. Of course it can be legit in the end, but there is just to much off and I'm almost certain someone just tried really really hard. Anyway, just calm down since there are not many ways they can get me so it's an interesting thing to share.