postfix-dovecot via lmtp

[Timothy Murphy]

I've been trying for some days to get postfix + dovecot + pigeonhole/sieve
working on a CentOS-7 home server.
I think I may have detected the problem; I read in /var/log/maillog
  Aug  4 11:29:13 alfred postfix/lmtp[14871]: 9C04C220A99:
    to=<tim at localhost.gayleard.eu>, orig_to=<tim at localhost>,
    relay=alfred.gayleard.eu[private/dovecot-lmtp], delay=971,
    delays=971/0.03/0.02/0.1, dsn=4.3.0, status=deferred 
    (host alfred.gayleard.eu[private/dovecot-lmtp] said: 451 4.3.0
    <tim at localhost.gayleard.eu> Internal error occurred. 
    Refer to server log for more information. (in reply to RCPT TO command))
(I've split one long line here.)

1) I see that the permissions on /var/spool/postfix/private/ are
  [tim at alfred ~]$ ls -ls /var/spool/postfix/
  4 drwx------.  2 postfix root     4096 Aug  4 11:30 private
The socket dovecot-lmtp setup by postfix is in this directory;
does dovecot need permission to access this?

2) I see that this mail (a test email from me) was deferred.
What exactly does this mean?
Where is the mail stored? I couldn't find it anywhere.
(It has already been brought to the server by fetchmail.)

3) Am I right in thinking that there are 2 alternatives to dovecot/sieve
  a) amavisd-new with postfix + spamassassin
  b) postfix + procmail ?

4) I remember seeing a posting (probably not in this mailing list)
describing how one can trace the progress of email through the server.
Unfortunately I didn't note the URL, and now cannot find it.
Does anyone have a pointer to such a document?

As will probably be obvious, I am not at all clear
how postfix and dovecot fit together if one introduces lmtp.
I take it that without lmtp (or similar) postfix just delivers email
to ~/Maildir/cur (in my case),
and dovecot is not involved at all until a client (KMail in my case)
looks at email?


-- 
Timothy Murphy  
e-mail: gayleard /at/ eircom.net
School of Mathematics, Trinity College, Dublin 2, Ireland