I set a qmail, vpopmail server with vpopmail-5.3.23. and config it as:
./configure \ --enable-roaming-users=n \ --enable-logging=p \ --enable-defaultquota=20971520S \ --enable-ip-alias-domains=n \ --enable-domainquotas=y \ \ --enable-passwd=n \ --enable-clear-passwd=y \ \ --enable-mysql=y \ --enable-incdir=/usr/include/mysql \ --enable-libdir=/usr/lib/mysql \ --enable-many-domains=y \ \ --enable-auth-logging=y \ --enable-mysql-logging=y \ --enable-valias=y \ --enable-mysql-limits=y
I don't see any default domain defined above.
-- Aj. Systems Administrator / Developer