Was a professor correct to chastise me for writing "Prof. X" rather than "Professor X"? I emailed Professor X regarding typos in, and questions on, his book. I've never met and contacted him. My email commenced with this salutation:


  Dear Prof. X


He replied


  It is customary to address professors by their title in full, just as most people would not abbreviate the full names of people whom they do not know well. 


His unpleasantness startled me. Is he correct though? If he is, wouldn't we have to write Mr. in full as Mister or even Master? 

My response to comments:

I'd rather not impart more particulars on Prof. X, in case he persecutes me! I'll just say that he's Caucasian, and in Australasia, North America or UK. English is definitely his native language.
What a jerk! No, writing "Prof." is perfectly fine; his reaction is both incorrect and completely inappropriate. I cannot imagine any professor I know (even the ones I don't like) writing such a thing. 

What country is this guy in? Some countries (e.g., Germany) have stricter rules for such things, but I'm still shocked he would respond like this.


  regarding typos in ... his book


Ah. Is it possible he's being snarky about your abbreviation since you criticized his typos? If your e-mail had a condescending tone, maybe he is trying to "bite back." That's the only thing I can think of.