[Dovecot] Intermittent timeout issues

[Del Stoliker]

Greetings list!

We've been experiencing an intermittent issue in which none users are able to log into the mail server for about 10 to 20 minutes.

This issue first appeared on our CentOS 4 box running dovecot 1.2.11 after upgrading from the stock version 0.99.  The issue persists after migrating our users to a CentOS 5 server - also running version dovecot 1.2.11 but now in the 64-bit flavor.

Our users authenticate against LDAP via PAM in case that might be relevant.

I've yet to find anything "of interest" in the logs covering the outages.  But here is what I've noticed:

* Users on our internal network are still able to authenticate and login.
* Users from the outside are "Disconnected for inactivity"
* Immediately after the restart, external users were able to log in again.

It almost sounds like the firewall is blocking external access except that:
* The version of dovecot was the thing that changed
* Everything starts working again after a dovecot restart

If anyone could provide some insight, I'd sure appreciate it.

Output of dovecot -n
# 1.2.11: /etc/dovecot.conf
# OS: Linux 2.6.18-164.15.1.el5 x86_64 CentOS release 5.4 (Final) 
listen: *
shutdown_clients: no
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
login_process_per_connection: no
login_trusted_networks: x.x.x.x/x
login_max_processes_count: 164
max_mail_processes: 2048
mail_max_userip_connections: 50
mail_location: maildir:~/Maildir
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/lib64/dovecot/imap
mail_plugin_dir(imap): /usr/lib64/dovecot/imap
mail_plugin_dir(pop3): /usr/lib64/dovecot/pop3
pop3_no_flag_updates(default): no
pop3_no_flag_updates(imap): no
pop3_no_flag_updates(pop3): yes
pop3_client_workarounds(default): 
pop3_client_workarounds(imap): 
pop3_client_workarounds(pop3): outlook-no-nuls oe-ns-eoh
lda:
  postmaster_address: postmaster at domain.com
  sendmail_path: /usr/sbin/sendmail
auth default:
  passdb:
    driver: pam
  userdb:
    driver: passwd