I would think that in 2011 it is common knowledge that both male and female students have reason to correspond with their college professors, and that male professors are able to exchange email messages with single females without fear of any suspicion of inappropriate behavior. Indeed, even in Saudi Arabia, which is far more restrictive in its mores/laws/conventions regarding women,
a 2006 study by the University of Jordan deemed acceptable for female students to correspond with male professors, as long as they phrased their text appropriately using the standard respectful/polite wording that is expected in face-to-face communication.
That said, I think that alfabeni should subtly indicate her gender by signing her next email to the professor "First Name Last Name (Miss)" (or Ms. or Mrs., whichever is appropriate). I feel certain that the professor's error is one of innocent ignorance, probably because alfabeni's gender is not immediately apparent from her given name. I have had to do the same with my own signature countless times over the years both in academic and business correspondence, because apparently my first name doesn't automatically indicate "I'm a girl!!" :-D