Great! Rated 5 out of 5 stars
you'd think things like Enigmail would be the default/norm/standard method for email. but its not. It is a shame enigmail isn't included with thunderbird by default as well... but that's been said a million times, enough about that.
Enigmail is a add-on that transforms email, rather than Thunderbird. With Enigmail, you generate a key that can be used to identify/authenticate you, yourself. It means you can 'sign' your email with this key, and it can be 3rd party verified that it really did come from you and no one else. If any/every email was done this way... you could feel confident that when your bank emailed you, (or other very sensitive matter), it really came from them. Email scams would nearly cease to exist. Spam would follow just as quickly and email would be more like personal mail.
The second benefit (if you choose) of Enigmail is full encryption. Lets face it, Gmail admins must read your email, if they don't, then maybe the don't, but its my word against theirs... but those ads that seem to know what your emails about didn't get that way from someone guessing, and who knows what metrics they keep on what ads they've sent to you (after all, that know its you, your email address doesn't change). Full encryption means without the key (think of it as a password that only receiver gets to know), no one can read your email.