The main window
Note how each email is displayed as an icon rather than in a boring list. You can modify an icon and the sound that is played when an email arrives for each person in your address book. The bottom half of the window shows the selected email's contents and who else it was sent to. It's laid out very clearly with the names of all the recipients of this email listed in alphabetical order. If you hover the mouse over a name the person's email address will appear as a tool tip, and you can right click on a name to bring up a list of actions.

The Address Book
This is where you select an icon, a sound and which folder you want emails from people you know to be dismissed to. You can also enter other contact details like phone numbers, address and web site. Adding people to the address book is easy - just click the mouse on a name in an email's recipient list and an entry is automatically created for you! You can sort the people in your address book in order of name, icon or how many emails you've sent to that person or received from them.

Icons
Choose an icon for people in your address book. If you want to you can use the same icon for all people at work or for a group of friends to make it easy to see at a glance who an email has been sent from.

Sounds
Choose a sound for people in your address book. This sound will be played when you receive an email from that person.

Groups
You can make groups out of people in your address book so that you can easily email those people all at once. You can quickly create a group by selecting the "Make the recipients of this email into a group" option and you can manually modify a group by just clicking on a person's name and press the 'Add' button to move them in or the 'Remove' button to move them out of the group.