[Dovecot] Dovecot fails almost every 20 minutes exactly

[Patrick - South Valley Internet]

Hi all,

We just set up our new mail servers using Postfix and Dovecot.  We have 
implemented a load balanced solution to where our two mail servers have 
a common NFS share.

Everything is working great.  Everything but Dovecot for the most part.  
In testing, Dovecot was great.  Now that we're in the production 
environment, we've noticed that every 20 minutes, Dovecot will stop 
running.  But it gets even weirder - it appears that Machine A will 
stop, then 20 mins later after we issue a 'service dovecot restart', 
Machine B will stop.  Then the whole process starts over when we restart 
Dovecot on Machine B.

I can't see anything out of the ordinary in the log files either.  I'm 
at a loss as to what's going on.

Here's my dovecot -n:

################################
# 1.0.3: /etc/dovecot.conf
listen: *
ssl_cert_file: /usr/share/ssl/hermes.garlic.com/hermes.garlic.com.cert.pem
ssl_key_file: 
/usr/share/ssl/hermes.garlic.com/hermes.garlic.com.privatekey.pem
login_dir: /var/run/dovecot-login
login_executable(default): /usr/libexec/dovecot/imap-login
login_executable(imap): /usr/libexec/dovecot/imap-login
login_executable(pop3): /usr/libexec/dovecot/pop3-login
first_valid_uid: 200
mail_location: maildir:/home/%u/Maildir:INDEX=MEMORY
maildir_copy_with_hardlinks: yes
maildir_copy_preserve_filename: yes
mail_executable(default): /usr/libexec/dovecot/imap
mail_executable(imap): /usr/libexec/dovecot/imap
mail_executable(pop3): /usr/libexec/dovecot/pop3
mail_plugin_dir(default): /usr/lib/dovecot/imap
mail_plugin_dir(imap): /usr/lib/dovecot/imap
mail_plugin_dir(pop3): /usr/lib/dovecot/pop3
auth default:
  user: dovecot-auth
  username_format: %Lu
  passdb:
    driver: pam
  userdb:
    driver: passwd
  socket:
    type: listen
    client:
      path: /var/spool/postfix/private/auth
      mode: 432
      user: postfix
      group: postfix
################################

Any ideas what could be wrong?  I don't think that setting up a cron to 
restart both dovecot servers is an idea solution - I'm hoping this is an 
easy fix.

Thanks in advance.

Patrick