Searching sent emails!
It happens sometimes that I have to find a reply I sent to someone, but checking it out in the sent mail folder is usually a mess. Well, Mail has a pretty cool way of finding it quickly. When you reply to someone's email, Mail will add a small arrow at the left of the email you just replied to. That's very useful to quickly see which email you already answered. Well it turns out that this arrow has even more use than that. You can click on it and it'll bring up your reply. There's no need of searching through the "Sent Mail" folder to find it anymore! Take a look on the screenshot here: