Ok so this is a bit silly, but it has made me wonder more than once. So I generally start the first email in a thread with proper salutations Dear "Dr. Fake name; Ms. Amanda Holdandhug", but I notice that they tend to write back with my first name. "Hi Lisa thank you for your email..." and often close with the valediction of their first name, "Sincerely, Amanda" I wonder if at the point, when I write back to them, should I transition to "Hi Amanda" (more cordial) or stick with "Thank you Ms. Holdandhug" (more professional). It's a silly dilemma but I'd like some input nonetheless.