# arg 1:  the new package version
post_install() {
  groupadd -g 79 exim &>/dev/null
  useradd -u 79 -g exim -d /var/spool/exim -s /bin/false exim &>/dev/null
}

# arg 1:  the new package version
# arg 2:  the old package version
post_upgrade() {
  post_install $1
}

# arg 1:  the old package version
pre_remove() {
  userdel exim &>/dev/null
  groupdel exim &>/dev/null
}

op=$1
shift

$op $*