Symptom
An alert box appears with the message:
"Logout has timed out because the application Mail failed to quit. To try again, quit Mail and choose Log Out from the Apple menu."
Figure 1 Mail failed to quit message
This happens if you choose Log Out from the Apple menu with the Mail application still open.
Solution
Quit Mail prior to logging out.
Sometimes Mail takes longer than expected to quit, a known behavior for this release of Mail. It does not indicate an issue. This may be addressed in a future software version.