I'm totally new to Mac (longtime Windows user) and I have a question about keyboard shortcuts in Mac OS X. Under Windows, I could access any menu item via the Alt key plus a series of letters corresponding to the menu selections. For example, I use Thunderbird for email, and the menu choice to see only unread messages is View | Threads | Unread I could access this option in Windows with the keyboard combination Alt-V (for View), then E (for Thr*e*ads), then U (for Unread). I can't figure out any corresponding way under OS X to get to this menu option via keystrokes. Is there a general mechanism for keystroke combinations to get menu options under OS X?