Bold letters means that the person is yelling at you. I use it to get the persons attention..
All CAPS is yelling, not bold. Bold is used to stress that word. As in "hug", a bold hug would be a "big hug" as opposed to a small hug. Duh!?!?
Bold letter means simply to emphasized or highlighting what you are trying to imply.
Bold,Red capital letters means the person is yelling. I have had this experience on a professional job and informed that the person using this format is yelling.