CentOS 6, cyrus-imapd 2.3.16-15.el6, postfix 2.6.6-8.el6, procmail 3.22-25.1.el6_5.1, squirrelmail 1.4.22-5.el6

[Adam Tauno Williams]

> Squirrelmail and (local for now) imapd.  But I cannot figure out how
> to either get cyrus-imapd to either access the local mail spool
> (/var/spool/mail) 

You can't.  Cyrus virtuously replaces /var/spool/mail.  Postfix
delivers mail into Cyrus, which stores it - and the **ONLY** way mail
is accessed is via Cyrus (IMAP, POP, JMAP).

You should configure Postfix to deliver to Cyrus via LMTP (local mail
transport protocol).

mailbox_transport = lmtp:unix:/var/lib/imap/socket/lmtp

[root at aleph ~]# fuser -u /var/lib/imap/socket/lmtp
/var/lib/imap/socket/lmtp:  4611(cyrus) 23327(cyrus)

> mailboxes.  When I forcably use deliver to try to deliver mail
> (manually  calling the deliver program, it says the mailboxes don't
> exist.  cyradm says  they do, but cannot reconstruct them or make sub
> mailboxes (permission denied).  Very strange.  What am I missing?

I haven't used deliver in decades.  Using LMTP avoids all the hazards
of old-school 'file processing'