Hello Mark,
in general spam efficiency reports would not work for individual, mainly because the spam detection process is not only limited to the spam engine, the major work is actually done by the reputation engine. In other words, senderbase, which on average blocks more that 90% of all connection attempts, mostly from hosts with a score of -5 or worse. By default these connections are already dropped before sender and recipients are injected, so the system is not aware who the potential spam was targeted for.
You could work around this by enabling delayed HAT rejection, which would still wait until sender and recipients are injected, before disconnecting. In this case, you can check
GUI: Monitor->Incoming Mail
specify a time range, and then enter the internal user in the search field below the main table. Or leave it empty and just hit "Search" for a list of all users, the list then can be sorted by clicking on the column names. The result table will contain entries like "Total Attemted" and "Spam Detected", and of course the results can be exported as well.
Hope that is what you are looking after.
Regards,
Andreas