WAG would be similar issues you can face when using NFS with multiple servers accessing it (file locking issues). The solution would be to use Director to make sure users are always directed to the same server. http://wiki2.dovecot.org/Director If that isn't the problem, then much more info would be needed (ie, doveconf -n output, logs exhibiting the problem, etc)...
Best regards,
*/Charles /*
Thank you for your reply. To further expand the problem does not happen with any regularity, we went over 30 days with no issue after two weeks of sporadic occurrences. It usually only appears, if at all, any time after 2:00 PM (i.e. 14:30, 15:20, 16:10). And not every day (has not happened on a weekend). The number of POP3 and IMAP processes increase dramatically when the issue occurs.
Here is a copy of the dovecot -n output
# 1.2.17: /usr/local/etc/dovecot.conf # OS: FreeBSD 8.1-RELEASE-p5 i386 nfs protocols: imap imaps pop3 pop3s ssl_cert_file: /mail/shared/etc/ssl/certs/dovecot.pem ssl_key_file: /mail/shared/etc/ssl/private/dovecot.pem disable_plaintext_auth: no login_dir: /var/run/dovecot/login login_executable(default): /usr/local/libexec/dovecot/imap-login login_executable(imap): /usr/local/libexec/dovecot/imap-login login_executable(pop3): /usr/local/libexec/dovecot/pop3-login login_greeting: Hello there, who might you be? max_mail_processes: 4096 verbose_proctitle: yes first_valid_uid: 26 first_valid_gid: 0 mail_privileged_group: mail mail_location: maildir:/mail/store/%d/%n mmap_disable: yes dotlock_use_excl: no mail_nfs_storage: yes mail_nfs_index: yes lock_method: dotlock mail_executable(default): /usr/local/libexec/dovecot/imap mail_executable(imap): /usr/local/libexec/dovecot/imap mail_executable(pop3): /usr/local/libexec/dovecot/pop3 mail_plugin_dir(default): /usr/local/lib/dovecot/imap mail_plugin_dir(imap): /usr/local/lib/dovecot/imap mail_plugin_dir(pop3): /usr/local/lib/dovecot/pop3 imap_client_workarounds(default): delay-newmail outlook-idle netscape-eoh tb-extra-mailbox-sep imap_client_workarounds(imap): delay-newmail outlook-idle netscape-eoh tb-extra-mailbox-sep imap_client_workarounds(pop3): pop3_client_workarounds(default): pop3_client_workarounds(imap): pop3_client_workarounds(pop3): outlook-no-nuls oe-ns-eoh lda: postmaster_address: {REMOVED} sendmail_path: /usr/local/sbin/exim auth default: default_realm: {REMOVED} username_format: %Lu passdb: driver: sql args: /mail/shared/etc/dovecot-sql.conf userdb: driver: passwd userdb: driver: static args: uid=26 gid=6 home=/mail/store/%d/%n