lmtpd delivery problem: User unknown

[Kai Lanz]

I'm trying to set up IMAP on a Tru64 4.0G box running sendmail 8.12.7,
patched.  We have hundreds of users, who currently use a mix of pine,
elm, and POP clients to read their mail.  We want to give them the option
of using IMAP clients as well.

Following the steps in install-configure.html, I made a new config file
for sendmail with definitions and rules for the cyrusv2 mailer.  If 
I start up master and then switch sendmail over to the new config file,
mail delivery stops working.  The mail.log shows "User unknown" for all
delivery attempts by cyrusv2; if there's a dead.letter, it contains a
more verbose error: "Mailbox unknown.  Either there is no mailbox 
associated with this name or you do not have authorization to see it."
The local6.log file only shows lmtp startup and shutdown messages.
Master is running, and so is lmtpd.

To me it looks like lmtpd can't write to our system inboxes under
/var/spool/mail.  Probably a permissions problem; so we reset the files
in this directory to be owned by group "mail" with group RW permissions.
That didn't help; we still get the User unknown complaint.

What's the right way to do this?  That is, to add IMAP service to our 
host without breaking pine et al.  Is lmtpd supposed to take care of this?
Can I turn up the debugging level on lmtpd to get a more detailed idea of
what's actually going on?