Formal:
* Cher/Chère: This is the most common and formal way to address someone in a letter or email. It's used for both men and women.
* Madame/Monsieur: You can use this if you are writing to someone formally. It's always followed by their last name.
Informal:
* Mon cher/Ma chère: This is a slightly more intimate way to address someone. It's used for both men and women.
* Cher/Chère + first name: This is a more casual way to address someone.
* Salut/Coucou: These are informal greetings you can use with friends or family.
Examples:
* Formal: "Cher Monsieur Dupont, ..."
* Informal: "Ma chère Marie, ..."
* Very casual: "Salut Sophie, ..."
Remember to choose the appropriate term based on your relationship with the recipient and the formality of the situation.