Thus, do I make it "Dear Mike, dear Prof Miller"? Or should I rather stick with "Dear Dr Smith, dear Prof. Miller" to be on the safe side?
Thanks for your advice.
Dear Dr. Smith & Dr. Miller,
You generally would only use firstnames in the "dear X" line of a letter, for people who are married or are in the same family: e.g. "Dear Jan and Tom,"
Also, I would use the same titles for both people: Dear Dr. Smith & Dr. Miller
(You could hardly offend someone by giving them the title "Dr.", even if they don't have their doctorate.) People rarely use the title "Prof." in writing, just as you would not address a letter to an actor named John Smith as Actor Smith. You would use "Mr. Smith". "Mr." is applied to all males, and "Mrs." or "Miss" are applied to females. So you could say: "Dear Mr. Smith & Mr. Miller". You could also write out their entire names if you wished, but I would recommed against using just the first names, as you don't know whether they know each other or not.
Feebs11I would disagree about addressing a Professor in the UK as anything but Prof. It is an official position and should be given its correct honorific. However, only do so if you are absolutely sure that the person in question is in fact Professor.Interesting. Over here, "professor" is mostly a spoken title, and is applied to university teachers whether or not they technically have the official position of Professor, rather than for example, Lecturer or Assistant Professor (although generally it would not not be used for teaching assistants.) It would not be used in an informal e-mail from a student to a professor. Also, over here it would be slightly offensive in a letter to write out the title of one professor, and use just the firstname of the other, rather than using Prof. for both.
Is "Mr. John and Jane Doe" appropriate?
Write 'Mr John and Mrs Jane Doe' if they are husband and wife, or
'Mr John and Ms Jane Doe' if they are brother and sister, or
'Mr John Doe and Ms Jane Doe' if they are unrelated but just happen to have the same surname.