If you need a really fast email client, very much handy one,  you should check with this new kid on the block of email clients, named Geary.

Its fast, faster than Thunderbird, its handy, very much useful and behave like you login on web interface of your email. It supports all of those main features like composer with spell check, sent, spam etc etc.

Its written in Vala language and its a GNOME project but surely you can install it to non-GNOME enivronments. Check out more about GEARY here