Is the expression "see you soon" impolite when I send email to superiors?
Solution 1:
You could certainly make the comment feel more formal. Length usually implies formality, so adding in some of the implicit words might help, or perhaps choosing different words. Even adding one word can feel less casual: "I'll see you soon."
If it's intended to be a workplace-polite way of saying, "this is the end of my message and I'd like to emphasize that I feel positive about our upcoming joint project/venture/meeting," I'd probably go with something more specific to the situation, such as "Looking forward to our meeting," or "I'll see you in the conference room."
If it's just a quick acknowledgement that you're about to meet them to discuss something non-critical, but you want to sound businesslike, then maybe "I'll be there shortly," or "I'll see you in a moment."
If you wish to communicate that you are doing as told, then perhaps you'd say, "I'll be there promptly," "I'm on my way," or "I'll be right there." In some jobs, where obedience is expected, you might add "sir" or some other contextually-appropriate label.