The Preferences option is available in either Geary's application menu or the gear menu in the upper-right of the toolbar. (The location depends on the install desktop shell. For GNOME Shell and Unity, the application menu is available near the top-left corner of the screen.)
When this option is enabled, Geary automatically selects the latest message in a folder when you enter the folder. In addition, after archiving a message, Geary automatically selects an adjacent message.
Enables message previews in the conversation list. Previews show the first few lines of each message.
When set, Geary automatically spell checks a message as you write it, underlying each misspelled word in red.
When set, Geary plays a sound whenever a new message arrives.
When set, Geary displays a notification each time a new message arrives. Notifications are displayed in a system-dependent manner. On GNOME Shell, notifications appear at the bottom of the display. In Ubuntu Unity, notifications appear at the upper right of the display.