Re: postfix connects to dovecot lmtp socket, but nothing is delivered

service lmtp { inet_listener lmtp { address = 127.0.0.1 port = 24 }

unix_listener /var/spool/postfix/private/lmtp { mode = 0660 user = postfix group = postfix }

Looks like you are activating both a socket and a port. Im not sure what dovecot does, does it bind to both or does it pick one and ignore the other. You only need to use one or the other.

And what does your postfix side look like? Where is postfix trying to connect? To the socket or the port? For using a socket postfix would look something like:

 virtual_transport = lmtp:unix:private/lmtp