This window pops up when you have reminders for calendar events, todo items or have set a follow-up on an email.
You can choose to dismiss the reminders or have the reminder return at a later time.
Reminder menu
Dismiss
Remind Later
Move to folder...
Sleep
Open...
Reply to sender
Forward
Delete
Undelete
Reply to all
Forward as attachment(s)
Ctrl-alt-f
Export...
Properties...