The default log level is 4. Lower values give more detail. Performance can be adversely affected when you run at log level 3 (SemiVerbose) or lower.
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\FaxcomMalboxServer\Parameter LogLevel REG_DWORD value with a default value of 4
You can set the size of the log files before rolling over in the registry on the Mailbox server:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\FaxcomMalboxServer\Parameter LogSizeMB REG_DWORD value with a default value of 10 (MB)
Whenever the service starts, the service checks the registry entry for SaveLogsOnStart. If the value is not zero, the Mailbox Server creates a folder in the Logs directory and moves the current log collection into that new folder.
After starting (as maybe saving the logs) the service sets the SaveLogsOnStart value to 1. When the service shuts down safely, it sets the SaveLogsOnStart value to 0. Saving the logs in the Logs folder is an indication of an abnormal shutdown or crash of the Mailbox Server service.