@waitingforcfe: I agree with you, Mercury is more professional. On the other hand has Mercury just a domain and a user list, and every user is getting mail for every domain. HMail has completely separated domains and you can create users for each domain.
In comparison with Postfix + dovecot both programs are just toys
Additional important thing is, that HMail stores everything inside an MySQL-Database. That's pretty useful, except that it does not provide the same flexibility like Postfix's + MySQL.
According to the huge amount of questions here in the forum, i would prefer some more "stupid-safe" mailserver in XAMPP. On the other hand should someone, who is not able to configure an mailserver like Mercury, not be allowed to operate an mailserver...