A future version of Mozilla's email client, Thunderbird, will receive tabs as reported by ZD Net. You can check out this new feature in Thunderbird 1.6 Alpha 1 available from Myk Melez, a Thunderbird developer. Tabs work much the same way as they do in Firefox and can even be dragged and dropped. I think this is a much needed feature for Thunderbird and I can't wait to see its final release.