I just installed Thunderbird so I could view emails from all my accounts at the same time. However, when I opened the program, each individual email is showing up separately even when they have the same sender. How do I make Thunderbird group emails into threads, so they don't take up so much space? I have multiple conversations going at any given time, and when they show each individual message, it doesn't take long to lose the thread of the conversation if the most recent from that person is buried under ten messages from another person.