mboxstats creates several top-10 lists from a file containing message
in mbox-format.  List of top10 lists:

o Top writes
o Top receivers
o Top subjects
o Top cc'ers
o Top top-level-domain
o Top timezones
o Top organisations
o Top useragents (mailprograms)
o Top month/day-of-month/day-of-week/hour
o Average number of lines per message
o All kinds of per-user statistics

And much more!

WWW: http://vanheusden.com/mboxstats/