Assuming you're looking for potential vulnerabilities or tricks related to HMailServer, here are a few: HMailServer, by default, allows unauthenticated SMTP relaying, which can be exploited to send spam emails. An attacker can use tools like telnet or swaks to test if the mail server is vulnerable.
To exploit the unauthenticated SMTP relay vulnerability, an attacker can use the following command: hmailserver hacktricks
swaks --to <recipient_email> --from <sender_email> --server <hmailserver_ip> --port 25 here are a few: HMailServer