A French professional email is more formal than an English one, and its frame is largely fixed:

Part	French	English
Greeting — named reader	Bonjour Madame, / Bonjour Monsieur Garnier,	Dear Ms …, / Dear Mr Garnier,
Greeting — unknown reader	Madame, Monsieur,	Dear Sir or Madam,
Opening	Je vous remercie de votre message.	Thank you for your message.
	Suite à notre conversation,…	Further to our conversation,…
Body	Vous trouverez ci-joint…	Please find attached…
Closing	Je reste à votre disposition pour tout renseignement complémentaire.	Please don't hesitate to contact me if you need any further information.
Sign-off	Cordialement, / Bien cordialement, / Bien à vous,	Kind regards, / Best regards, / Best wishes,

Chère Madame and Cher Monsieur are warmer — for someone you already know. After the greeting comes a comma, and the next line starts with a capital.