Usage of "Dear"

[LeiYee]

I'm a girl. Can I use Dear to a man, my officer, who is not very friendly with me?

 

[Rover_KE]

No, unless you are writing a formal letter to him, in which case you would begin 'Dear Mr Horrid'.

 

[LeiYee]

I'm sorry that I'm not clear.

You replied me "No". What does it mean?
I can use or I can't use.

 

[charliedeut]

He means that, since you dislike the person in question (hence his "Dear Mr. Horrid), you would only want to use it as the opening formula in a polite letter. Otherwise, you have no reason to use it, since it is usually a term for people you love/like/are fond of.

 

[LeiYee]

Oh! I see.
I think I miss some information. I want to write an email to my officer, upper level officer.

According to the replied answers, I can use "Dear Mr. A," as opening formula in my email. Is that right?
many thanks.

 

[charliedeut]

Yes, that is right.