How To Write A Letter Dear Sir . If you are writing to a person in a company whose name you don’t know, you can start with “dear sir / madam”. Sir john smith (and the appropriate letters after the name) spouse of a knight. Formal letter Sara from www.slideshare.net Martin haynes or dear ms. Writing dear professor smith or dear dr. Every letter, email or communication should start with a salutation if it is addressed to someone.