I have to write an email to a group of 3 professors: 2 men and 1 lady. My question is how to say hello to them properly? I often use only 'Bonjour' or 'Bonjour à tous' but I find that not polite enough.
I thought about: "Bonjour madame et messieurs" or "Bonjour professeurs" (or "Bonjour les professeurs"? please correct me on this one).