Regarding the dreaded Pegasus mail (which I use and actually like
quite a bit), users need to do two things to prevent the confirmation
messages.  Senders of a message should never use the "confirm
reading" or "confirm delivery" options when sending a message.
Also, all users have an "allow confirmation requests" option that they
can turn off.  When its off, their system won't send out
confirmations even if another message comes in with a confirmation
request on it.  Also, I believe its true that this problem only
involves Pegasus mail systems interacting with one another.