[Dovecot] dovecot-auth Temporary But Frequent CPU Spike

[Joe Clark]

Hi.. I am setting up a new server (2GHz CPU, Ubuntu 8.10) and am using 
dovecot for an IMAP server.  I have installed dovecot 1.1.4 and 
Squirrelmail 1.4.15.  sudo dovecot -n shows this:

# 1.1.4: /etc/dovecot/dovecot.conf
log_timestamp: %Y-%m-%d %H:%M:%S
protocols: imap
login_dir: /var/run/dovecot/login
login_executable: /usr/lib/dovecot/imap-login
login_process_per_connection: no
mail_privileged_group: mail
auth default:
  passdb:
    driver: pam
  userdb:
    driver: passwd

The problem I'm noticing is that if I do top -d 1 while clicking links 
in Squirrelmail (e.g., logging in, the Inbox link, opening a message), I 
see that a "dovecot-auth" process maximizes the CPU for about a second.  
While this is not a huge amount, it seems like with multiple users it 
could quickly bog down a server .

Are there any recommendations or thoughts on what might cause the 
one-second CPU spike?  -- or is that just normal operation?  Thanks for 
your thoughts.
- Joe Clark