I think that you just went too fast. You need to slow down, and take things one step at a time. You have a sophisticated Postfix configuration. Trying to integrate maildrop in a custom environment, such as that, without previous experience is just not going to work. First, you should try to get maildrop working with ordinary /etc/passwd accounts. Once you're comfortable

There's nothing in maildrop's code that "finds the virtualhosts", whatever that means. Again, you must be referring to some feature that are particular to whatever custom version of maildrop you installed. You should go back and read the documentation for that feature, also. There's a slight chance that someone on this list might recognize the specific custom version of maildrop you're running, but that's not very likely.