The Mail Source Agent contains an informational message such as the following:
"08/04/2008 03:22:27 FolderFilter::ExcludeFolder TraceMsg 2301 Excluding folder \Calendar because it is excluded by the user"
What does this mean?
This is an informational message which actually means that the Calendar will not be processed by the Mail Source Agent as calendars are in fact processed by the Calendar Source Agent instead.
The message is normal and can be safely ignored.