I don’t know if there is a notifier option available…. but yes you could run a simple script like
# NOT TESTED!
#!/bin/bash
echo "Updatecheck Mailcow"
updateexist="$(cd /opt/docker/mailcow-dockerized | ./update.sh --check | tail -n 1)"
if [ "$updateexist" = "Updated code is available." ]
then
echo "Mailcow Update available" | mail -s "INFO: Mailcow Update available" test@example.com <<< "Mailcow update.sh output: $updateexist"
fi