Updated doxygen for Mail get API

Author: evedon

rtos/Mail.h

@@ -200,11 +200,12 @@ class Mail : private mbed::NonCopyable<Mail<T, queue_sz> > {
      *
      * @param millisec Timeout value (default: osWaitForever).
      *
-     * @return Event that contains mail information or error code.
-     * @retval osEventMessage   Message received.
-     * @retval osOK             No mail is available (and no timeout was specified).
-     * @retval osEventTimeout   No mail has arrived during the given timeout period.
-     * @retval osErrorParameter A parameter is invalid or outside of a permitted range.
+     * @return Event that contains mail information and status code. The status code
+     *         is stored in the status member:
+     *         @a osEventMail      Mail successfully received.
+     *         @a osOK             No mail is available (and no timeout was specified).
+     *         @a osEventTimeout   No mail has arrived during the given timeout period.
+     *         @a osErrorParameter A parameter is invalid or outside of a permitted range.
      *
      * @note You may call this function from ISR context if the millisec parameter is set to 0.
      */