Hi,
I have 3 users for 1 domain so the count is easy.
In the Daily mail report I can see :

41 messages found for 41 recipients
Most active senders = 41 (2 from inside, 39 from outside)

but
Most active recipients = 138 (9 outside, 129 inside (and one guy = 121 !))

so what ?

I use zcs-3.1.4_GA_518.FC4.tgz + sqlgrey-1.6.7