ACL syntax for setting specified folders within Maildir/ read-only for owner

[kepa]

Hi,

I have dovecot (2.2.16, see dovecot -n at end) installed to /opt on 
CentOS 6 for access on a local network. I would like to create an 
archival mail account which will reduce the primary account file size 
and still make older emails easily accessible. How can I set specified 
folders in this Maildir read-only with ACL? For example, I included this 
in the dovecot-acl file to specify protected folders in the archives@ 
Maildir but it did not work:

"Email 2013/*" user=archives lrs
"Email 2014/*" user=archives lrs

Also tried this on folders without spaces with no success (the folders 
were still delete-able by the user via the Thunderbird client). Each 
"Email..." folder has several child folders that should also be read-only.

BTW, what is the maximum size for a Maildir that Dovecot can comfortably 
handle?

Thanks!

Kepa

dovecot -n:
# 2.2.16: /opt/dovecot/etc/dovecot/dovecot.conf
# OS: Linux 2.6.32-504.12.2.el6.x86_64 x86_64 CentOS release 6.6 (Final)
mail_location = maildir:~/Maildir
mail_plugins = acl
namespace inbox {
   inbox = yes
   location =
[mailbox info ...]
     plugin {
   acl = vfile:/opt/dovecot/etc/dovecot/dovecot-acl
}
protocols = imap
service imap-login {
   inet_listener imaps {
     port = 993
     ssl = yes
   }
}
ssl_cert = </etc/ssl/certs/dovecot.pem
ssl_key = </etc/ssl/private/dovecot.pem
userdb {
   driver = passwd
}
protocol imap {
   mail_plugins = acl imap_acl