I'm using maildrop as a transport in postfix to handle virtual
mailboxes. When I inject a message to go to one of these virtual
mailboxes, I get the following error in the maillog:
(temporary failure. Command output: /usr/bin/maildrop: Invalid home
directory permissions - world writable. )
^^^^^^^^^^^^^
Where is the home directory? You proved that the maildir is not world
writable, but that is not what the log message is about.
How you set the home directory for virtual users depends on many
factors. You didn't reveal anything of your setup: configuration files,
operating system, its version, Postfix version, Maildrop version,
database back-end type (LDAP/RDBMS), its implementation or version.
What permissions should the /home/vmail directory and the virtual
mailbox directories inside of that be?
chown -R vmail:vmail home/vmail
Virtual mailboxes typically (some say "by definition") have the same
uid:gid, though most systems let you define uids in the database (to
enforce file system quotas for example).
You need to tell your MDA to run as user vmail as well.