I am aware that in Japanese it is considered to be rude to address other people with just their first name, but I wonder if this is only true for communication in Japanese, of if this still holds true when communicating with Japanese people in other languages than Japanese like for example in English.
I am especially interested in business communication in industries that use to prefer rather informal communication between business partners in the western world.
For example in the computer games industry a typical email would just be started with "Hi recipientsFirstname" and ended with something like "Kind regards, sendersFirstname", even when addressing people that one has never talked to before and no matter of where in the world the recipient is from, except when it comes to Japanese people. Whenever the recipient is Japanese, then even for English mails most colleagues try to get more formal and start their email with either "Hi recipientsLastname-San" or just "Hi recipientsLastname" (interestingly, Mr./Mrs./Ms. always gets left out), but they still end it with something like "Kind regards, sendersFirstname".
Now this looks very strange to me and feels just terribly wrong.
Am I even supposed to attach "San" to the name, even when I am not writing in Japanese, but in English, even in the most informal industries?
What about this weird mix of addressing the recipient with his/her last name, but using only the own first name in the greeting, so that in worst case (if he/her can't get it from anywhere else and its neither contained in the signature nor in the email-address of the sender) the recipient would not even know the senders last name?
PS: I am aware that this is more a question about the Japanese culture and etiquette than about the Japanese language, but unfortunately those don't have there own stackoverflow communities. Please move this question if there is a more appropriate community for it than "Japanese Language".