Thunderbird. It's fast, provides native UI elements, and allows for an information dense presentation of a lot of information. Works great for handling multiple email accounts viaimap.
i like that i can just ignore my email completely, and only open it when i want to. so i use gmail in browser.<p>i have considered using thunderbird but... i dont really email that much.<p>for work it's outlook and outlook only. i dont like it but it works.