ENDLESS SPAMMING FROM BOB@GMAIL.COM

I just launched my site last week, and since day TWO, I’ve been bombarded by Russian SPAM — all of which includes the email addy “Bob@Gmail.com” — My email box is jammed FULL of spam comments, which I dutifully “mark as spam” or “delete” — but they keep coming back! What gives and can anyone offer me some insight into making this go away — once and for all?