Postfix Ignoring lmtp, delivering straight to maildir

[Doug Barton]

First I'd like to thank all the developers and contributors to dovecot. 
I've been using it for many years, and deeply appreciate your fine work. :)

dovecot --version
2.2.22 (fe789d2)

I have a working installation with postfix and dovecot, and I want to 
add sieve to it, so I am trying to configure postfix to use lmtp instead 
of 'virtual' for its delivery service. However it is ignoring that 
request, and for every message I get "status=sent (delivered to 
maildir)" and it shows up in my Inbox.

On my mail host I have 1 normal user, let's say the username is 
'myuser'. I have postfix configured to accept mail for several different 
domains, and each domain has a lot of different mail usernames (I use 
this for mailing lists and such). I use the virtual_maps feature of 
postfix, and have a map file that looks like this:

abuse at dougbarton.us myuser
hostmaster at dougbarton.us myuser
dougb at dougbarton.us myuser
...

All of this works great, and mail for all the different usernames and 
domains gets delivered into my one real user's Maildir, and I can see 
the mail with my IMAP clients.

I've configured sieve in dovecot, and I can see the socket for lmtp in 
/var/spool/postfix/private/. I can also see the managesieve port in 
netstat, and I can use a sieve client to connect to it and edit scripts, 
etc.

So according to all the tutorials I've read my next step is this in 
postfix' main.cf:

virtual_transport = lmtp:unix:private/dovecot-lmtp

which I did, and postfix restarts with no errors. But, it seems to avoid 
lmtp altogether, and as I mentioned above it delivers straight to my 
Maildir Inbox every time.

I do have a sieve file, and the ~/dovecot.sieve symlink exists. I 
created a very simple filter:

require ["fileinto", "imap4flags"];

if header :contains "Subject" "test"
{
   fileinto "Junk";
}

which my sieve client says is correct syntax. Still no joy. :-/

Any thoughts or suggestions are welcome. (And sorry this is so long, but 
based on my extensive searches it seems my configuration is a bit 
unique, so I explained it in some length.)

Doug