After using Thunderbird for more than a year, I switched back to Outlook. Why? It was the little inconveniences like inability to step through emails which I overlooked until now.
Anyhow, I ran though hoops trying to move messages from Thunderbird to Outlook, all of them partially successful but always droping something. In the end, I just bought Aid4Mail. It's ironical that I spent $50 to stop using a free email client.
Between the Cathedral and the Bazaar are the Twisted Alleys.