Suppose I need to write an letter (email, actually), addressed to two academicians. One is a full professor, and the other does not yet have this title. What is a polite way of opening the letter?
If the letter was to be addressed to just the professor, it would certainly be proper to open with "Dear Professor Smith". If the letter was just to the not-yet-professor, I suppose it would be acceptable to open with either "Dear Professor Jones" (using a higher title for politeness) or "Dear Doctor Jones" (using his proper title).
What happens if you need to address the two people at once in a polite way? It seems that addressing Jones as Doctor would draw attention to the fact that he does not yet have professorship. On the other hand, addressing Jones as Professor leads to him and Smith being given the same title, and Smith might not like that.
Of course, in almost all circumstances this is a non-issue, since neither Jones nor Smith will pay much attention. But given how many conventions there are for writing letters, I somehow feel there should be a rule also for situations such as this one. Is there one?