Boomerang for Gmail is a powerful extension that can help you make sure to follow up with important emails.
One of Boomerang’s most powerful features is tracking responses. When writing an email, you can set Boomerang to give you a reminder if you don’t get a reply after a certain amount of days. If the message comes back to your inbox without a response, you can then react by sending another email to follow up.
You can schedule your follow-up message as you're writing the original email. If the person replies to your original email, Boomerang will detect the response, and will not send the second email. If they don’t reply, Boomerang will send the follow-up message automatically, without you having to think about it.