Any idea what linux kernel versions might cause this?
(from main dovecot webpage news) Thu Mar 22 14:38:53 EET 2012Red Hat/CentOS users: A recent kernel update <https://bugzilla.redhat.com/show_bug.cgi?id=681578> causes Dovecot to start failing after it has reached 1000 child processes. To fix this, downgrade your kernel until Red Hat releases a fixed kernel.