[Dovecot] dovecot scaling issue?

[it-dovecot at ml.epigenomics.com]

Hi!

We are running dovecot-imapd on Debian sarge out of the backports.org
packages (version 1.0.rc15-1~bpo1).

We have ~ 80 clients using secure IMAP.

I understand that imap-login has to run for every SSL connection. Thus I
already increased the max value for the number of imap-login processes.

But unfortunately dovecot is unresponsive from time to time. Where can
I tune the installation? Do I need to upgrade to 1.0.0, for which no
backported packages exist for Debian sarge?

This is the output of dovecot -n:

log_timestamp: %Y-%m-%d %H:%M:%S 
listen: *:143
ssl_listen: *:993
ssl_cert_file: /etc/courier/imapd.pem
ssl_key_file: /etc/courier/imapd.pem
disable_plaintext_auth: no
login_dir: /var/run/dovecot/login
login_executable: /usr/lib/dovecot/imap-login
login_processes_count: 12
login_max_processes_count: 512
verbose_proctitle: yes
mail_location: maildir:~/.Maildir:INDEX=/var/cache/dovecot/INBOX.%u:CONTROL=/var/cache/dovecot/INBOX.%u
mail_full_filesystem_access: yes
maildir_stat_dirs: yes
maildir_copy_with_hardlinks: yes
namespace:
  type: private
  separator: .
  prefix: INBOX.
  inbox: yes
namespace:
  type: public
  separator: .
  prefix: shared.
  location: maildir:~/.Maildir/shared:INDEX=/var/cache/dovecot/shared.%u:CONTROL=/var/cache/dovecot/shared.%u
auth default:
  verbose: yes
  passdb:
    driver: passwd
  userdb:
    driver: passwd

Homedirectories are on NFS, /var/cache/dovecot is a local filesystem.
Clients are mostly Thunderbird, where max connection to IMAP server is
set to 5.

Greetings
-- 
Robert Sander                     Senior Manager Information Systems
Epigenomics AG    Kleine Praesidentenstr. 1    10178 Berlin, Germany
phone:+49-30-24345-0                            fax:+49-30-24345-555
http://www.epigenomics.com             robert.sander at epigenomics.com