use dovecot lmtp for transport

templates/main.cf.j2

@@ -52,9 +52,8 @@ virtual_mailbox_maps =
    proxy:mysql:/etc/postfix/sql/mysql_virtual_mailbox_maps.cf,
    proxy:mysql:/etc/postfix/sql/mysql_virtual_alias_domain_mailbox_maps.cf
 
-# if you let postfix store your mails directly (without using maildrop, dovecot deliver etc.)
-#virtual_mailbox_base = /var/mail/vmail
-# or whereever you want to store the mails
+# use dovecot lmtp for mail transport
+virtual_transport = lmtp:unix:private/dovecot-lmtp
 
 # Additional for quota support
 #virtual_create_maildirsize = yes