Look up his CV or some of his recent work and see how he titles himself then follow suit. I recommend a thoughtful handwritten request with a brief (and genuine) explanation of why you chose him.
Honestly, email is your best bet. I have yet to meet an academic that didn't prefer that form of communication. Just be aware that his .edu may be filtered by a grad student/admin and you may get a form response.
I haven't encountered that often but because some of his works appeal to the armchair historian he may have had to do that.