Do i address him as doctor?

Yes, Dr. is the appropriate title in your email. Dr. is preferred over Professor. Different schools have different customs when it comes to "Prof" some prefer only "Full" Professors be addressed as such. Also, if the person isn't at a university (or holds an admin title), they shouldn't be referred to as Prof. Therefore Dr. is always the safest was to go. That said, most of us don't care if someone calls us Dr. or Mr/s.