claws-mail-aur-hsh-patch/claws-mail.install

post_upgrade() {
  if [ "`vercmp $2 4.0.0`" -lt 0 ]; then

cat << _EOF
  >>> If you are upgrading from the GTK+ 2 version to the GTK+ 3 version
  >>> of Claws Mail, you will need to reload any plugins that you want to use.
_EOF

 fi
}