Mr. Mayor
Salutations are gestures or greetings that are meant as an acknowledgment. The proper salutation for a current mayor is Mr. Mayor or Madam Mayor.
"Your Honor" or "Mr. (Mrs.) Mayor"
Dear Mr. Mayor or sometimes, such as New York, Your Honor.
'Dear Mayor Smith' is acceptable for ordinary communication. 'Your Honor' is a more formal salutation. In Canada (and, I think, in Britain also) it might be better to use 'Your Worship.' (A mayor historically had the powers of a magistrate.) Check with the municipality's office of protocol when in doubt.
Mr and Mrs would be proper. Attorneys are typical written to as Mister.
Dr. and Mr. Smith
madame mayor
Dear Mr. John and Rev. Sally Smith,
Dear Mr. Guy and Dr. Girl
The proper salutation for a husband and wife who are both doctors is "Drs. [Husband's Last Name] and [Wife's Last Name]." If they share the same last name, it can simply be "Drs. [Last Name]." Alternatively, you can address them as "Doctors [Husband's Last Name] and [Wife's Last Name]" if you prefer a more formal approach.
The mayor is generally referred to as Sir, or Mister Mayor. His wife, unless she holds a political office herself, is called Mrs. Whatever-her-last-name-is. - wjs1632 -