I am an assistant professor outside the US. I want to email an associate professor in another university in the US, who I haven't talked to before. He's American. It's just because I want to discuss his paper. I agree with his paper, so the discussion will be most likely "nice".
Which is better? "Dear Professor {last name}" or "Dear {first name}"?
Does your answer change if he's a young assistant professor or an old almost-retiring full professor?
When in doubt, play it safe.
Addressing the professor using "Professor (lastname)" will do no harm to anyone, while some may take offence to using the first name. In any first instance of communication, I always advocate the formal tone of "Dear Professor", and keep an eye on their articulation of the salutation. If they write
Email content bla bla ...
Best regards,
First-name
then that is your sign to start addressing the person by their first name (in case they are superior/senior). If they do not, continue with the formal tone. In the other case, if you happen to be senior, use the common tactics in military: address an unknown junior officer with a formal tone, then when they reply, start using their first name to show that the seniority has been established.
I'm in CS, and my exchanges are always like this: I start with "Dear Dr X, my name is First-name Last-name, and here's who I am and what I contact you about. Best regards, Firstname". This is both respectful and, at the same time, sets the tone that you aren't interested in pointless formalities. Without exception, the exchange continues like this: they reply with "Dear Firstname, ..., Regards, Charles", I reply with "Hi Charles".
In the US, the only time "Dear {first name}" is appropriate is when communicating between established friends, coworkers or family. It is never appropriate in any professional setting -- academia or business -- until you actually are established friends.
Prof.
In my experience this is the standard academic address to someone you don’t know. E.G., This is what journal editors tend to use when asking for reports. No one is likely to be offended. Even in countries where more complicated/formal titles are the norm.
Of course, “Hi” or “Dear” are mostly fine too. But I have heard of (older?) people being offended on occasion.
