A Question of Message Etiquette

Since finding this subreddit, I have been made aware of a wide variety of reasons why someone might not respond to a first message. Now, if someone still has an account and still seems interesting:

• Would you try contacting them again?
• If so, after how long (e.g., one week is too short, but a month is okay)?
• Have you had any success with a second try at first contact?