I'm often asked a tricky but important question about business communication:
"When should I be formal or informal with my business emails?"
Tone is perhaps the toughest aspect of email writing. Since the person on the other end can't hear us say the words, they have to assume our intent or inflection. And so often, they guess wrong.
"Is she trying to be funny? That message came off rude."
"I thought he was a nice guy? His emails are so cold."
Or more to the point:
"He's way too comfortable with his messages to our team. Not professional at all."
When you move from a formal to informal tone, you roll the dice and hope the other person will appreciate your casualness.