I sometimes get emails (e.g. from professional contacts or people I don't know well) which simply start with
[ ... letter body ... ]
They don't use "Dear FirstName," or "Hello FirstName," just "FirstName,".
This always feels quite harsh to me. (Omitting the opening completely in a quick email wouldn't feel that way, but using the name only does.)
Can this be considered impolite? Is it bad form? Is it usual? What should I read into this (about the attitude of the writer)?
I realize that these things can depend more on the culture than the language. I usually get these letters from Americans. Is it the most usual way of opening an informal email in the U.S.?