There are various articles that refer to logging level 7.
262308 XCON: How to Generate Application Log Events for Non-Delivery Report
http://support.microsoft.com/?id=262308
is an example. Benjamin, logging level 7 is actually a higher level of logging then what you can set in the MMC. Maximum in the MMC is equivalent to logging level 5. Within PSS we use logging level 7 to trap a higher level of detail. It is not an available option in the GUI and not spoken of much because it typically will cause so much information to dump that it could be harmful to performance if left that way permanently. Generally we will only go to logging level 7 if we can not establish any other indicators of why an error is happening.