Sometimes, Mac bugs just drive me crazy. The solution tricks are listed below for memo.
Always 1 unread notification in the mailbox.
add a URL to dock
only work via safari :https://support.apple.com/en-us/HT201719
change default app
right click file and get Info: http://www.imore.com/how-change-default-apps-os-x
delete all ipad photoes from Mac
spotlight-> image capture