I don't know what's in the file, but I can tell you where you got it from because I have one too (and I was very angry when I saw it
). Or, to be exact, I have that email file
only in the "The Sims 3" folder I used to download free stuff from inside the game. The last feature of Shop Mode where they introduced with the last patch, and that let you see free/paying items (with yellow borders) in the various Build/Buy/CAS modes in game.
My file is dated from January 16th, and the .sims3pack I downloaded have the same date too.
In the other "The Sims 3" folders I have (I use your factory reset tip), there is no email file, but they have never connected to the web either.
I don't know if it's safe to delete though. I'd assume yes, but one never knows...
This kind of file is the very reason I'm not much thrilled by the new features of Showtime, certainly when some of them will come with the patch itself. (Yes, I'm a tad paranoid sometimes
)