In latest version of qmail that change certain values.
Example, think hostname as 'server.domain.com'. In previous content of /var/qmail/control/me (also defaulthost and defaultdomain) is 'domain.com' but in latest is 'server.domain.com'.
Need changed because will be trouble with 'delegate' subdomain to other server. Let say, domain.com in VPS1 but vps2.domain.com in VPS2.
To minimize issue, add 'A record' for subdomain of hostname. Example, add 'server' for 'A record' in 'domain.com' dns.