I accidentally learned a new Gmail trick today. I was viewing an email and accidentally hit the 'm' key on my keyboard. This apparently mutes the conversation making that thread disappear from your inbox. This is a cool trick on its own, but what happens if you want to unmute it? In your Gmail search you can enter: is:muted, and you will see a list of all muted threads. To unmute, click into one and choose "Move to Inbox" in the select box at the top.