Right behind the update to Firefox, the Mozilla crew has bumped resident email/news/RSS client Thunderbird to version 18.104.22.168. Several security and bugfix changes are included. You can lift your wings and download it at mozilla.org.
I will admit that I've never used Thunderbird on a regular basis, as I am bound to Entourage/Exchange at work and I've gotten (reluctantly) used to it. Email clients are like your barber; even if the haircut isn't that great, switching to a new one involves a degree of discomfort. I'd be interested to hear what T-bird users like or dislike most about their feathery friend. (No John Travolta jokes.)