It's better than free options like Eudora Lite or Outlook Express, but it's not as robust as a pay email program may be. Nonetheless, it has brilliant Bayesian spam filtering and good news/RSS features.
Perusal of newsgroups also works well with Thunderbird.
I've used Thunderbird for a little over a year now and am not disappointed. I switched to it for its Bayesian filtering. My junk mail filter has 164 spams in it at this time, from the last few days. It has never (to my knowledge) mistakingly flagged a message as junk. It doesn't flag 100% of the spam, but a good 95+% of it, I'd say, which saves me time. I have it set up with 6 email accounts. It allows multiple SMPT servers, and works flawlessly with Gmail after configured. Filters are well implemented. I've not used it with newsgroups. Mine is currently using around 1400K minimized. .
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