Yes, Yahoo briefcase is legit, and the email is probably legit as well. Just go to briefcase.yahoo.com and see if you have anything in it. If you do, then copy the files if they are of any use. We all have briefcases as part of our Yahoo account, but few people ever used it.

Regarding whether you got an email or not, the message was probably caught in a spam filter. Lots of email from Yahoo is (for obvious reasons: so many spammers use it).

I just looked at mine. I have 4 folders, 3 empty and one which has an mp3 named testcase.mp3 from 2003. I don't think I need that! And, no, I don't remember storing it there but I undoubtedly did. I remember little from 2003 ... or 2004 ... or ... oh, nevermind.