Nowadays, there is a trend to avoid the use of the formulas "Dear Sir or Madam" or "Dear Sir/Madam"in the beginning of a formal letter. One may use "To whom it may concern" instead. There are even other alternatives which are more suitable.
The problem is that not everyone will identify with “Sir” or “Madam”. To quote
(...) You never want to offend or assume the gender conformity of a business associate or peer. If you do guess a contact’s gender -- and guess wrongly -- you’ll immediately raise red flags and risk your ability to do business with them.
My question is if the alternative formulas
Aux personnes intéressées/aux personnes concernées
À l'attention des personnes intéressés/concernées
Merci de communiquer ces informations aux personnes intéressées/concernées
share the same "neutrality" as the English counterpart "To whom it may concern".