Like in the hypernode-vagrant project, all emails are caught and redirected to a MailHog instance. You can visit the mailhog web interface on port 8025. So for example, if the IP of your container is 172.17.0.2 you would be able to access MailHog on http://172.17.0.2:8025/.
Alternatively you could set up a hosts entry like so on the host (not in the Docker):
grep -q hypernode.hypernode.local /etc/hosts || echo "172.17.0.2 hypernode.hypernode.local" >> /etc/hostsAnd then visit the MailHog instance on http://hypernode.hypernode.local:8025.