I should have mentioned that this is not iPhone specific, the same behaviour may be observed for 2 simultanious connections from 2 separate machines running Thunderbird.
TLS/SSL is used on both.
dovecot config file below:
Nigel
# 1.2.9: /etc/dovecot/dovecot.conf # OS: Linux 2.6.18-028stab069.5 x86_64 Ubuntu 10.04 LTS log_timestamp: %Y-%m-%d %H:%M:%S protocols: imaps login_dir: /var/run/dovecot/login login_executable: /usr/lib/dovecot/imap-login mail_privileged_group: mail mail_location: maildir:~/Maildir mailbox_idle_check_interval: 5 mbox_write_locks: fcntl dotlock auth default: mechanisms: plain login passdb: driver: pam userdb: driver: passwd socket: type: listen client: path: /var/spool/postfix/private/auth-client mode: 432 user: postfix group: postfix