Granted right now Thunderbird is not as feature packed as Outlook. But Thunderbird 2 will be adding several new features such as the new message alert indicator, message tags and may be even tabs. Thunderbird 2 will also render incoming HTML e-mails via Firefox. Outlook 2007 (due out in February) on the other hand is not going to use Internet Explorer anymore to render incoming HTML E-Mails. Nope, it is going to use the MS Word rendering engine which is currently uses for creating e-mails. So what you ask? First off, ever try to make a web page out of…