1. This is my favorite: If you press J and K on the email list or while reading the email, it moves between previous and next emails in the context. (just like in the vi 😉 )
2. While reading and email, if you press N it goes to the next email, P to the previous email. And if you press same keys on the email list, it goes next day and previous day consecutively.
3. Space key and Shift+Space key scrolls page by page the email list, or the email.
4. T and B are shortcuts for Top and Bottom, no more scrolling like crazy to go to the end of an email 🙂
5. R is to Reply, L is to Reply All.
6. U is to go to the oldest unread messages.

I hope this is useful 😉