Formal letters

[Unregistered]

What is the right formal way to write the salutations in a letter for a man and a woman at the same time?
For exemple I have to send a letter to Mr. Sanders and Mrs. Smith, should I write:
Dear Mrs. Smith and dear Mr. Sanders,
or
Dear Mrs. Smith/Mr. Sanders,
Thank you in advance for your answer.

 

[Anglika]

Dear Mr Sanders and Mrs Smith

OR

Dear Mrs Smith and Mr Sanders