On various occasions through out the years of running
an xoops site, I've occasionally had circumstance where
the private message system has been used to bully other
members, or just mail general abuse.
as the site owner, it's then my responsibility to
investigate, which involves long hard searching through
the database.
An option for admins to be able to investigate private
messages, maybe admin access to all private messages.
Or an option whereby a user can report the private
message, and allow admin access to the accounts for
investigation