if they ask you to give them any info it's a scam. I suggest tracking the IP; if its a scam the IP will likely be in russia or africa or some other odd locale.
that looks authentic, but as dominion said, email addresses can be spoofed.. if it asks for info of any sort, it's a fake, if it doesn't, just check to see if your games are still playable, if they aren't, then maybe you need to re-purchase them, tho i've never heard of something like that before.. Just to make sure, contact Steam as to what you should do!
thats really wierd try e-mailing them back if you can tos ee whats going on and if they ask for info just ignore them or mark the e-mail as phishing scam