We have been asked over 100 times now to let our members on the site see the status of their sent messages. We also understand the personal implications of that as well.
But something that is widely requested would be to allow the members (allow for enabling all levels in billing options) to see whether their message sent was Read, Unread, Replied To, or Deleted.
The configuration should allow for enabling all of these and also on a billing option basis.
Generally people want to know, are we being heard? Even rejected gracefully by no reply after being read..
But allow the admins to turn it off if necessary.