You can install Sort Gmail Inbox from Sort Gmail Inbox from Chrome Web Store.

To see all contacts you are awaiting a reply from select:

• Click on Sorted Sent Mail
• Click on Contacts – Awaiting Reply

How to remove a contact form the Contacts – Awaiting Reply list?

• Click on Sorted Sent Mail
• Click on Contacts – Awaiting Reply
• Click on the triangle menu icon on the right side of a particular contact to open the menu.
• Click on Ignore / Mark it as done

• Click on Sorted Received Mail
• Click on Contacts – Not Replied
• Click on the triangle menu icon on the right side of a particular contact to open menu.
• Click on menu item Ignore / Mark it as done

• Click on the triangle menu icon on the right side of a particular contact to open menu.
• Click on menu item Setup text & SMS alerts for a particular contact…